An Etymological Dictionary of Astronomy and Astrophysics

That can be done or used or put into practice.

See also: → practice; → -able.

That can be done or used or put into practice.

See also: → practice; → -able.

Concerned with practice, as opposed to → theory.

See also: → practice; → -al.

Concerned with practice, as opposed to → theory.

See also: → practice; → -al.

1a) To do habitually or regularly.

1b) To exercise or follow as a profession.

2a) Performance; the doing of something (contrasted with → theory). See also → praxis.

2b) Way of doing something that is common or habitual.

2c) Frequent or systematic repetition in doing something.

Etymology (EN): M.E. practisen, practizen;
O.Fr. practiser “to practice,” from M.L. practicare “to do, perform,” from L.L. practicus “practical,” from Gk. praktikos “practical.”

Etymology (PE): 1) Varzidan “to practice, perform; to accustom oneself to; to labor; to sow a field;” Mid.Pers. warz- “to work, do, practice;” Av. varəz- “to work, do, perform, exercise;” cf. Gk. ergon “work;” Arm. gorc “work;” Lith. verziu “tie, fasten, squeeze,” vargas “need, distress;” Goth. waurkjan; O.E. wyrcan “work,” wrecan “to drive, hunt, pursue;” E. work;
PIE base *werg- “to work.”

2. varzé, noun from present stem varz- + suffix -é.

1a) To do habitually or regularly.

1b) To exercise or follow as a profession.

2a) Performance; the doing of something (contrasted with → theory). See also → praxis.

2b) Way of doing something that is common or habitual.

2c) Frequent or systematic repetition in doing something.

Etymology (EN): M.E. practisen, practizen;
O.Fr. practiser “to practice,” from M.L. practicare “to do, perform,” from L.L. practicus “practical,” from Gk. praktikos “practical.”

Etymology (PE): 1) Varzidan “to practice, perform; to accustom oneself to; to labor; to sow a field;” Mid.Pers. warz- “to work, do, practice;” Av. varəz- “to work, do, perform, exercise;” cf. Gk. ergon “work;” Arm. gorc “work;” Lith. verziu “tie, fasten, squeeze,” vargas “need, distress;” Goth. waurkjan; O.E. wyrcan “work,” wrecan “to drive, hunt, pursue;” E. work;
PIE base *werg- “to work.”

2. varzé, noun from present stem varz- + suffix -é.

Actively following a specified career or way of life.

See also: → practice; → -ing.

Actively following a specified career or way of life.

See also: → practice; → -ing.

A professional man, especially in medicine and the law.

Etymology (EN): Alteration of practician, → practice (+ -ian)

• -er, → -or.

Etymology (PE): Varzmand, from varz, → practice, + -mand, → -ist.

A professional man, especially in medicine and the law.

Etymology (EN): Alteration of practician, → practice (+ -ian)

• -er, → -or.

Etymology (PE): Varzmand, from varz, → practice, + -mand, → -ist.

An → open cluster in the constellation → Cancer containing about 50 stars of 6th magnitude or fainter. It lies 577 light-years away. Also called NGC 2632, the Beehive Cluster, or the Manger.

Etymology (EN): From L. praesepe “crib,” from which cattle or horses are fed, manger; the neighboring brighter stars Gamma and Delta Cancri (Asellus Borealis and Asellus Australis) were pictured as asses which fed from a manger.

Etymology (PE): Perâysepé, loan from L., as above.
Kandu “beehive; a large earthen vessel in which grain is kept;” cf. Skt. kunda- “a bowl-shaped vessel, basin; the lower abdomen.”
Âxor “manger,” prefixed xor “to eat” (semantically like E. manger, Fr. mangeoire, from L. manducare, mandere “to chew, eat”), from Mid.Pers. âxwarr; Av. avô-x^varəna- “drinking fountain; a water spring,” from avô- “water” + x^varəna-, from x^var- “to consume, eat;”
Mid.Pers. xvardan “to eat, enjoy (food);” Mod.Pers. xordan “to eat, drink, devour,” Laki dialect hovârden “to eat;” Proto-Iranian *huar- “to consume, eat.”

An → open cluster in the constellation → Cancer containing about 50 stars of 6th magnitude or fainter. It lies 577 light-years away. Also called NGC 2632, the Beehive Cluster, or the Manger.

Etymology (EN): From L. praesepe “crib,” from which cattle or horses are fed, manger; the neighboring brighter stars Gamma and Delta Cancri (Asellus Borealis and Asellus Australis) were pictured as asses which fed from a manger.

Etymology (PE): Perâysepé, loan from L., as above.
Kandu “beehive; a large earthen vessel in which grain is kept;” cf. Skt. kunda- “a bowl-shaped vessel, basin; the lower abdomen.”
Âxor “manger,” prefixed xor “to eat” (semantically like E. manger, Fr. mangeoire, from L. manducare, mandere “to chew, eat”), from Mid.Pers. âxwarr; Av. avô-x^varəna- “drinking fountain; a water spring,” from avô- “water” + x^varəna-, from x^var- “to consume, eat;”
Mid.Pers. xvardan “to eat, enjoy (food);” Mod.Pers. xordan “to eat, drink, devour,” Laki dialect hovârden “to eat;” Proto-Iranian *huar- “to consume, eat.”

Concerned with practical results and values; treating things in a practical way.

Etymology (EN): M.Fr. pragmatique, from L. pragmaticus “skilled in business or law,” from Gk. pragmatikos “versed in business,” from pragma (genitive pragmatos) “civil business, deed, act,” from prassein “to do, act, perform.”

Etymology (PE): Varzâl-gerâ, literally “practice-inclined,” from varzâl, → practical, + -gerâ “inclining toward, intending, making for,” → -ist.

Concerned with practical results and values; treating things in a practical way.

Etymology (EN): M.Fr. pragmatique, from L. pragmaticus “skilled in business or law,” from Gk. pragmatikos “versed in business,” from pragma (genitive pragmatos) “civil business, deed, act,” from prassein “to do, act, perform.”

Etymology (PE): Varzâl-gerâ, literally “practice-inclined,” from varzâl, → practical, + -gerâ “inclining toward, intending, making for,” → -ist.

A branch of → semiotics dealing with the relation between language and the users, especially the constraints they encounter in using language in social interaction, and the corresponding effects
on other users in the communication.

See also: → pragmatic; → -ics.

A branch of → semiotics dealing with the relation between language and the users, especially the constraints they encounter in using language in social interaction, and the corresponding effects
on other users in the communication.

See also: → pragmatic; → -ics.

Philo.: The doctrine that the truth or value of a concept or assertion is determined by its practical effects upon human interests.

See also: → pragmatic; → -ism.

Philo.: The doctrine that the truth or value of a concept or assertion is determined by its practical effects upon human interests.

See also: → pragmatic; → -ism.

A dimensionless number representing the ratio of the fluid viscosity to the thermal conductivity of a substance; a low number indicates high convection.

See also: Named after the German physicist Ludwig Prandtl (1875-1953); → number.

A dimensionless number representing the ratio of the fluid viscosity to the thermal conductivity of a substance; a low number indicates high convection.

See also: Named after the German physicist Ludwig Prandtl (1875-1953); → number.

1. The practice and practical side of knowledge or skills, as opposed to the → theory.
   

2. Accepted practice or custom.

Etymology (EN): M.L. praxis “practice, action,” from Gk. praxis “practice, action, doing,” from stem of prassein “to do, to act.”

Etymology (PE): Varzidâr, from varzid past stem of varzidan, → practice, + -âr prefix forming nouns of action, such as kerdâr, raftâr, didâr, goftâr, jostâr, etc.

1. The practice and practical side of knowledge or skills, as opposed to the → theory.
   

2. Accepted practice or custom.

Etymology (EN): M.L. praxis “practice, action,” from Gk. praxis “practice, action, doing,” from stem of prassein “to do, to act.”

Etymology (PE): Varzidâr, from varzid past stem of varzidan, → practice, + -âr prefix forming nouns of action, such as kerdâr, raftâr, didâr, goftâr, jostâr, etc.

A prefix meaning “before, prior to, in advance of, early, beforehand, in front of.”

Etymology (EN): M.E., from O.Fr. pré-, from L. præ (adverb) “before.”

Etymology (PE): Piš- “before; in front,” from Mid.Pers. pêš “before, earlier,” O.Pers. paišiya “before; in the presence of.”

A prefix meaning “before, prior to, in advance of, early, beforehand, in front of.”

Etymology (EN): M.E., from O.Fr. pré-, from L. præ (adverb) “before.”

Etymology (PE): Piš- “before; in front,” from Mid.Pers. pêš “before, earlier,” O.Pers. paišiya “before; in the presence of.”

A precursor of a small, loosely bound → star cluster (→ bound cluster) as well as an → OB association, with masses ranging from about 10 to 1000 → solar masses or more.

See also: → pre-; → cluster; → core.

A precursor of a small, loosely bound → star cluster (→ bound cluster) as well as an → OB association, with masses ranging from about 10 to 1000 → solar masses or more.

See also: → pre-; → cluster; → core.

Same as → PG 1159 star.

See also: → post-; → degenerate; → star.

Same as → PG 1159 star.

See also: → post-; → degenerate; → star.

A technique in spectroscopy which uses a combination of several dispersive elements (prisms in series or a grism) before focusing the light on the primary disperser, usually a grating, in order to achieve high spectral resolutions.

See also: → pre-; → dispersion.

A technique in spectroscopy which uses a combination of several dispersive elements (prisms in series or a grism) before focusing the light on the primary disperser, usually a grating, in order to achieve high spectral resolutions.

See also: → pre-; → dispersion.

A → Herbig AeBe star displaying → forbidden emission lines in its spectrum.

See also: → pre-; → main; → sequence; → B[e] star.

A → Herbig AeBe star displaying → forbidden emission lines in its spectrum.

See also: → pre-; → main; → sequence; → B[e] star.

A → binary system whose components are → pre-main sequence stars.

See also: → pre-; → main sequence; → binary.

A → binary system whose components are → pre-main sequence stars.

See also: → pre-; → main sequence; → binary.

A star that evolves in the → Hayashi phase and has not yet reached the → zero-age main sequence.

See also: → pre-; → main sequence,
→ star.

A star that evolves in the → Hayashi phase and has not yet reached the → zero-age main sequence.

See also: → pre-; → main sequence,
→ star.

The stage of a star before its eruption to become a nova.

See also: → pre-; → nova;
→ stage.

The stage of a star before its eruption to become a nova.

See also: → pre-; → nova;
→ stage.

An adjective relating to a stage before the formation of a → protostar. → pre-stellar core.

See also: → pre-; → stellar.

An adjective relating to a stage before the formation of a → protostar. → pre-stellar core.

See also: → pre-; → stellar.

A small, gravitationally unstable molecular → clump of typical size of less than 0.1 pc resulting from → gravitational collapse and → fragmentation of a larger → molecular cloud. It is a centrally concentrated structure which evolves into a → class 0 object, where eventually a single star or a stellar system is formed. Core masses range between 0.5 and 5 solar masses, with a mean number density of at least 10⁴-10⁵ cm^-3, and a temperature as low as about 10 K. A pre-stellar core evolves into a → Class 0 object. Also called dense core.

See also: → pre-stellar; → core.

A small, gravitationally unstable molecular → clump of typical size of less than 0.1 pc resulting from → gravitational collapse and → fragmentation of a larger → molecular cloud. It is a centrally concentrated structure which evolves into a → class 0 object, where eventually a single star or a stellar system is formed. Core masses range between 0.5 and 5 solar masses, with a mean number density of at least 10⁴-10⁵ cm^-3, and a temperature as low as about 10 K. A pre-stellar core evolves into a → Class 0 object. Also called dense core.

See also: → pre-stellar; → core.

A → post-planetary nebula star that is approaching the top of the → white dwarf sequence. These stars have exhausted the capacity of → nuclear burning in their cores.

See also: → pre-; → white; → dwarf.

A → post-planetary nebula star that is approaching the top of the → white dwarf sequence. These stars have exhausted the capacity of → nuclear burning in their cores.

See also: → pre-; → white; → dwarf.

Existing before or making possible the appearance of living organisms. Prebiotic molecules are biologically essential components
such as amino acids, sugars, and nucleic-acid bases which are precursors of the origin of life.

See also: → pre- + → bio- + -tic equivalent of → -ic.

Existing before or making possible the appearance of living organisms. Prebiotic molecules are biologically essential components
such as amino acids, sugars, and nucleic-acid bases which are precursors of the origin of life.

See also: → pre- + → bio- + -tic equivalent of → -ic.

1. To correct celestial coordinates for → precession.
   
2. To undergo → precession.

Etymology (EN): Back formation from → precession.

Etymology (PE): Back formation from pišâyân, → precession.

1. To correct celestial coordinates for → precession.
   
2. To undergo → precession.

Etymology (EN): Back formation from → precession.

Etymology (PE): Back formation from pišâyân, → precession.

The apparent position of a celestial object corrected for the epoch → precession.

See also: Precessed, p.p. of → precess;
→ coordinates.

The apparent position of a celestial object corrected for the epoch → precession.

See also: Precessed, p.p. of → precess;
→ coordinates.

The periodic motion of the → rotation axis of a
body such as a → spinning top in which the axis of rotation gradually sweeps out a conical shape. In the case of the spinning Earth, it is due to the combined → gravitational attractions of the → Sun, the → Moon, and → planets on Earth’s → equatorial bulge. Since
the Earth’s axis is tilted to its → orbital plane or
→ ecliptic, the gravitational force of the Sun and the Moon on the Earth’s equatorial bulge tend to pull it back toward the plane of ecliptic. As a result, the axis → precesses. Earth’s axis of rotation precesses with a period of about 25,770 years, describing
one complete circle on the → celestial sphere
(→ precession constant). This circle has a radius of approximately 23°.5, equal to the → inclination of the Earth’s orbit. Since the → vernal equinox is the reference direction for the → equatorial coordinate system, the coordinates of “fixed” objects change with time and must therefore be referred to an → epoch at which they are correct.
→ sign of zodiac.

See also → general precession; → precession of the ecliptic; → precession of the equator; → precession of the equinoxes; → precessional circle; → precession time; → geodetic precession; → general precession in longitude; → general precession in right ascension; → orbital precession; → perihelion precession; → planetary precession; → precession period.

Etymology (EN): L.L. præcissionem “a coming before,” from L. præcessus, p.p. of præcedere “to happen before,” from the fact that the equinoxes occur earlier each year with respect to the preceding year,
from præ- “before,” → pre-, + cedere “to walk, to go, to happen.”

Etymology (PE): Pišâyân, literally “coming before,” from piš- “before” → pre- + ây- (present stem of âmadan “to come, arrive, become”), from Av. ay- “to go, to come,” aēiti “goes;” O.Pers. aitiy “goes;” Skt. e- “to come near,” eti “arrival;” L. ire “to go;” Goth. iddja “went,” Lith. eiti “to go;” Rus. idti “to go;”

• -ân suffix of space and time.

The periodic motion of the → rotation axis of a
body such as a → spinning top in which the axis of rotation gradually sweeps out a conical shape. In the case of the spinning Earth, it is due to the combined → gravitational attractions of the → Sun, the → Moon, and → planets on Earth’s → equatorial bulge. Since
the Earth’s axis is tilted to its → orbital plane or
→ ecliptic, the gravitational force of the Sun and the Moon on the Earth’s equatorial bulge tend to pull it back toward the plane of ecliptic. As a result, the axis → precesses. Earth’s axis of rotation precesses with a period of about 25,770 years, describing
one complete circle on the → celestial sphere
(→ precession constant). This circle has a radius of approximately 23°.5, equal to the → inclination of the Earth’s orbit. Since the → vernal equinox is the reference direction for the → equatorial coordinate system, the coordinates of “fixed” objects change with time and must therefore be referred to an → epoch at which they are correct.
→ sign of zodiac.

See also → general precession; → precession of the ecliptic; → precession of the equator; → precession of the equinoxes; → precessional circle; → precession time; → geodetic precession; → general precession in longitude; → general precession in right ascension; → orbital precession; → perihelion precession; → planetary precession; → precession period.

Etymology (EN): L.L. præcissionem “a coming before,” from L. præcessus, p.p. of præcedere “to happen before,” from the fact that the equinoxes occur earlier each year with respect to the preceding year,
from præ- “before,” → pre-, + cedere “to walk, to go, to happen.”

Etymology (PE): Pišâyân, literally “coming before,” from piš- “before” → pre- + ây- (present stem of âmadan “to come, arrive, become”), from Av. ay- “to go, to come,” aēiti “goes;” O.Pers. aitiy “goes;” Skt. e- “to come near,” eti “arrival;” L. ire “to go;” Goth. iddja “went,” Lith. eiti “to go;” Rus. idti “to go;”

• -ân suffix of space and time.

The amount by which the equinoctial points drift westward annually due to precession. Its value for epoch J2000.0 is 50’’.26, resulting from the westward → precession of the equator (50".38), and the eastward → precession of the ecliptic (0".12).

See also: → precession; → constant.

The amount by which the equinoctial points drift westward annually due to precession. Its value for epoch J2000.0 is 50’’.26, resulting from the westward → precession of the equator (50".38), and the eastward → precession of the ecliptic (0".12).

See also: → precession; → constant.

The component of general precession caused by the gravitational attraction of the planets on the Earth’s center of mass. It causes the equinox to move eastward by about 0’’.12 per year in the opposite direction to
the → precession of the equator. This terminology replaces → planetary precession, according to an IAU resolution adopted in August 2006.

See also: → precession; → ecliptic.

The component of general precession caused by the gravitational attraction of the planets on the Earth’s center of mass. It causes the equinox to move eastward by about 0’’.12 per year in the opposite direction to
the → precession of the equator. This terminology replaces → planetary precession, according to an IAU resolution adopted in August 2006.

See also: → precession; → ecliptic.

That component of general precession caused by the combined effect of the Moon, the Sun and the planets on the equatorial protuberance of the Earth, producing a westward motion of the equinoxes along the ecliptic about 50’’ per year.
According to an IAU resolution adopted in August 2006, the present terminology replaces lunisolar precession.

See also: → precession; → equator.

That component of general precession caused by the combined effect of the Moon, the Sun and the planets on the equatorial protuberance of the Earth, producing a westward motion of the equinoxes along the ecliptic about 50’’ per year.
According to an IAU resolution adopted in August 2006, the present terminology replaces lunisolar precession.

See also: → precession; → equator.

The slow motion of the equinoxes along the ecliptic, resulting from the combined motion of the equator (→ precession of the equator) and the ecliptic (→ precession of the ecliptic), or in other words the precession of the Earth’s axis of rotation. Also know as → general precession. The First Point of Aries moves westward along the ecliptic at 50.38 arcseconds per year (1 degree every 71.6 years), causing the equinoxes to occur about twenty minutes earlier each sidereal year. See also → nutation.

See also: → precession; → equinox.

The slow motion of the equinoxes along the ecliptic, resulting from the combined motion of the equator (→ precession of the equator) and the ecliptic (→ precession of the ecliptic), or in other words the precession of the Earth’s axis of rotation. Also know as → general precession. The First Point of Aries moves westward along the ecliptic at 50.38 arcseconds per year (1 degree every 71.6 years), causing the equinoxes to occur about twenty minutes earlier each sidereal year. See also → nutation.

See also: → precession; → equinox.

The gradual change in he orbital planes of a binary system.

See also: → precession; → node.

The gradual change in he orbital planes of a binary system.

See also: → precession; → node.

The interval with which a rotating body precesses. The precession period of the Earth is 25,770 years. For a → spinning top it is given by: T_p = (4π²I)/(mgrT_s),

where I is the → moment of inertia, m the mass of the top, g gravity, r the distance between the center of mass and the contact point, and T_s is the spinning period of the top.

See also: → precession; → period.

The interval with which a rotating body precesses. The precession period of the Earth is 25,770 years. For a → spinning top it is given by: T_p = (4π²I)/(mgrT_s),

where I is the → moment of inertia, m the mass of the top, g gravity, r the distance between the center of mass and the contact point, and T_s is the spinning period of the top.

See also: → precession; → period.

A time interval over which an orbit precesses by 2π radians in its plane.

See also: → precession; → time.

A time interval over which an orbit precesses by 2π radians in its plane.

See also: → precession; → time.

Of or pertaing to → precession.

See also: → precession; → -al.

Of or pertaing to → precession.

See also: → precession; → -al.

The path of either → celestial poles around the → ecliptic pole due to the → precession of equinox. It takes about 26,000 years for the celestial pole to complete path.

See also: → precessional; → circle.

The path of either → celestial poles around the → ecliptic pole due to the → precession of equinox. It takes about 26,000 years for the celestial pole to complete path.

See also: → precessional; → circle.

1. Meteo.: Any form of water, such as rain, snow, sleet, or hail, that falls to the Earth’s surface. The quantity of such water falling in a specific area within a specific period.
   
2. Chemistry: The process of separating a solid substance from a solution.

Etymology (EN): From M.Fr. précipitation, from L. præcipitationem “act or fact of falling headlong, haste,” from præcipitare “fall, be hasty,” from præceps “steep, headlong, headfirst,” from præ- “forth” + caput, → head.

Etymology (PE): 1) Bâreš, verbal noun of bâridan “to rain,” bârân “rain;” Mid.Pers. vâritan, vârân; Av. vār- “rain; to rain;” cf. Skt. vār- “rain, water; to rain;” PIE base *uer- “water, rain, river.”
Rizeš, verbal noun of rixtan “to flow, to pour,” → overflow.

2. Tahnešast “to settle down, precipitate,” from
   tah “→ bottom, end;” + nešast past stem of nešastan “to sit down; to settle down; to sink,” → sit.

1. Meteo.: Any form of water, such as rain, snow, sleet, or hail, that falls to the Earth’s surface. The quantity of such water falling in a specific area within a specific period.
   
2. Chemistry: The process of separating a solid substance from a solution.

Etymology (EN): From M.Fr. précipitation, from L. præcipitationem “act or fact of falling headlong, haste,” from præcipitare “fall, be hasty,” from præceps “steep, headlong, headfirst,” from præ- “forth” + caput, → head.

Etymology (PE): 1) Bâreš, verbal noun of bâridan “to rain,” bârân “rain;” Mid.Pers. vâritan, vârân; Av. vār- “rain; to rain;” cf. Skt. vār- “rain, water; to rain;” PIE base *uer- “water, rain, river.”
Rizeš, verbal noun of rixtan “to flow, to pour,” → overflow.

2. Tahnešast “to settle down, precipitate,” from
   tah “→ bottom, end;” + nešast past stem of nešastan “to sit down; to settle down; to sink,” → sit.

1. Definitely or sharply stated, or defined.
   

2. Designating → precision.
   

See also: → accurate, → exact.

Etymology (EN): M.E., from M.Fr. précis “cut short” from M.L. precisus, from L. præcisus “abridged, cut off,” p.p. of præcidere “to cut off, shorten,” from præ- “in front,” → pre-,

• cædere “to cut down, chop, beat, hew, slay.”

Etymology (PE): Parsun literally “cut around” (compare with Skt. pariccheda “precise, accurate definition, exact discrimination,” from pari- + cheda “cut, cutting off,” from chid- “to cut, split”), from par-, variant of
pirâ- “around, about,” → peri-, + sun “to cut;” cf. Kurd. Sorani su, sun “to sharpen, whet;” Kurd. Kurmanji (prefixed ha-, contraction of *ham-) hasun “to sharpen, whet;” Mod.Pers. sân “whetstone,” variants fasân, afsân, awsân; Av. si-, sā- “to cut;” cf. Skt. śā- “to sharpen, whet” (see also → concrete).

1. Definitely or sharply stated, or defined.
   

2. Designating → precision.
   

See also: → accurate, → exact.

Etymology (EN): M.E., from M.Fr. précis “cut short” from M.L. precisus, from L. præcisus “abridged, cut off,” p.p. of præcidere “to cut off, shorten,” from præ- “in front,” → pre-,

• cædere “to cut down, chop, beat, hew, slay.”

Etymology (PE): Parsun literally “cut around” (compare with Skt. pariccheda “precise, accurate definition, exact discrimination,” from pari- + cheda “cut, cutting off,” from chid- “to cut, split”), from par-, variant of
pirâ- “around, about,” → peri-, + sun “to cut;” cf. Kurd. Sorani su, sun “to sharpen, whet;” Kurd. Kurmanji (prefixed ha-, contraction of *ham-) hasun “to sharpen, whet;” Mod.Pers. sân “whetstone,” variants fasân, afsân, awsân; Av. si-, sā- “to cut;” cf. Skt. śā- “to sharpen, whet” (see also → concrete).

In a precise manner.

See also: → precise; → -ly.

In a precise manner.

See also: → precise; → -ly.

The quality or state of being very accurate.

See also: → precise; → -ness.

The quality or state of being very accurate.

See also: → precise; → -ness.

1. The state or quality of being → precise.
   

2. The degree to which repeated measurements of a quantity give the same results under unchanged conditions. Not the same as → accuracy,
   but often confused as such. See → accuracy for the difference between precision and accuracy.

See also: Verbal noun from → precise.

1. The state or quality of being → precise.
   

2. The degree to which repeated measurements of a quantity give the same results under unchanged conditions. Not the same as → accuracy,
   but often confused as such. See → accuracy for the difference between precision and accuracy.

See also: Verbal noun from → precise.

1. A person or thing that comes before another of the same kind; a forerunner.
   

   2. A substance from which another is formed, especially by metabolic reaction (OxforddDctionaries.com)

Etymology (EN): M.E., from L. præcursor “forerunner,” from præcursus, p.p. of præcurrere, from præ- “before,” → pre-, + currere “to run,” → current.

Etymology (PE): Pišgâm, from piš- “before,” → pre-, + gâm “step, pace,”
→ stage.

1. A person or thing that comes before another of the same kind; a forerunner.
   

   2. A substance from which another is formed, especially by metabolic reaction (OxforddDctionaries.com)

Etymology (EN): M.E., from L. præcursor “forerunner,” from præcursus, p.p. of præcurrere, from præ- “before,” → pre-, + currere “to run,” → current.

Etymology (PE): Pišgâm, from piš- “before,” → pre-, + gâm “step, pace,”
→ stage.

A component of a → pulsar pulse that appears shortly in advance of the main pulse.

See also: → precursor; → pulse.

A component of a → pulsar pulse that appears shortly in advance of the main pulse.

See also: → precursor; → pulse.

1. Act of plundering or robbing; predatory behavior.
   

   2. The preying of one animal on others.

See also: Verbal noun, → prey.

1. Act of plundering or robbing; predatory behavior.
   

   2. The preying of one animal on others.

See also: Verbal noun, → prey.

Zoology: Any organism that exists by preying upon other organisms (Dictionary.com).

See also: Agent noun from → prey.

Zoology: Any organism that exists by preying upon other organisms (Dictionary.com).

See also: Agent noun from → prey.

1. Of, or relating to a predator.
   

   2. Living by preying on other living animals.

See also: Agent noun from → prey.

1. Of, or relating to a predator.
   

   2. Living by preying on other living animals.

See also: Agent noun from → prey.

1a) Grammar: The part of a → sentence or → clause stating something about the → subject and usually consisting of a → verb. For example, in the sentence “The man opened the door,” the subject is “the man” and the predicate is “opened the door.”

1b) Logic: Something which is affirmed or denied concerning the subject in a → proposition.

1c) Math.: A → function whose values are statements about n-tuples of objects forming the values of its → arguments. For n =1 a predicate is called a “property” , for n> 1 a → relation; propositions may be regarded as zero-place predicates (encyclopediaofmath.org).

2a) To state, affirm, or assert (something) about the subject of a proposition.

2b) To make (a term, expression, etc.) the predicate of a proposition.

Etymology (EN): M.E., from M.Fr. predicat, from L. praedicatus “declared, proclaimed,” p.p. of praedicare, from prae “beforehand,” → pre-,

• dicare “proclame,” from stem of dicere “to speak, to say,” from PIE root *deik- “to point out, to show,” cognate with Pers. dis, → form, and andišidan, → think.

Etymology (PE): Farâsan from farâ- “before; toward, along; above, upon, over,” → pro-, + san Proto-Ir. *sanh- “to declare, explain,” related to soxan, → speech and pâsox, → response, sahân, → sentence.

1a) Grammar: The part of a → sentence or → clause stating something about the → subject and usually consisting of a → verb. For example, in the sentence “The man opened the door,” the subject is “the man” and the predicate is “opened the door.”

1b) Logic: Something which is affirmed or denied concerning the subject in a → proposition.

1c) Math.: A → function whose values are statements about n-tuples of objects forming the values of its → arguments. For n =1 a predicate is called a “property” , for n> 1 a → relation; propositions may be regarded as zero-place predicates (encyclopediaofmath.org).

2a) To state, affirm, or assert (something) about the subject of a proposition.

2b) To make (a term, expression, etc.) the predicate of a proposition.

Etymology (EN): M.E., from M.Fr. predicat, from L. praedicatus “declared, proclaimed,” p.p. of praedicare, from prae “beforehand,” → pre-,

• dicare “proclame,” from stem of dicere “to speak, to say,” from PIE root *deik- “to point out, to show,” cognate with Pers. dis, → form, and andišidan, → think.

Etymology (PE): Farâsan from farâ- “before; toward, along; above, upon, over,” → pro-, + san Proto-Ir. *sanh- “to declare, explain,” related to soxan, → speech and pâsox, → response, sahân, → sentence.

The generic term for systems of → formal logic like → first-order logic and → second-order logic. Predicate logic contains → variables which can be quantified (→ quantify, → quantification).

See also: → predicate; → logic.

The generic term for systems of → formal logic like → first-order logic and → second-order logic. Predicate logic contains → variables which can be quantified (→ quantify, → quantification).

See also: → predicate; → logic.

In a → formal language, a letter used to describe a → predicate or → relation. Also called → relation symbol.

See also: → predicate; → symbol.

In a → formal language, a letter used to describe a → predicate or → relation. Also called → relation symbol.

See also: → predicate; → symbol.

To like better or value more highly.

Etymology (EN): M.E. preferre, from O.Fr. preferer and directly from L. praeferre “to place or set before, carry in front,” from prae “before,” → pre-, + ferre “to carry, to bear,” from PIE root *bher- “to carry;” cf. Pers. bordan “to carry, bear,” → refer.

Etymology (PE): Behzunidan, literally “to value highly, to consider better,” from beh “good, fine,” → optimum,

• zun, variant of dân-, dânestan “to know, consider,” cf. Tâti zun/zund “to know,” Khunsâri zûn-/zûnâ, Mahallâti zôn-, Semnâni -zûn-, Hamedâni zunayän/zun- , Esfahâni zunän/zun-, Yarandi zônâj-/zôn-, Gazi zûn-/zûnâšt;
  Av. zān- “to know,” → science.

To like better or value more highly.

Etymology (EN): M.E. preferre, from O.Fr. preferer and directly from L. praeferre “to place or set before, carry in front,” from prae “before,” → pre-, + ferre “to carry, to bear,” from PIE root *bher- “to carry;” cf. Pers. bordan “to carry, bear,” → refer.

Etymology (PE): Behzunidan, literally “to value highly, to consider better,” from beh “good, fine,” → optimum,

• zun, variant of dân-, dânestan “to know, consider,” cf. Tâti zun/zund “to know,” Khunsâri zûn-/zûnâ, Mahallâti zôn-, Semnâni -zûn-, Hamedâni zunayän/zun- , Esfahâni zunän/zun-, Yarandi zônâj-/zôn-, Gazi zûn-/zûnâšt;
  Av. zān- “to know,” → science.

Worthy to be preferred; more desirable.

See also: → prefer; → -able.

Worthy to be preferred; more desirable.

See also: → prefer; → -able.

1. Act of → preferring.
   

   2. That which is preferred.

See also: → prefer; → -ence.

1. Act of → preferring.
   

   2. That which is preferred.

See also: → prefer; → -ence.

An → affix that is placed before a base to denote a modified meaning or make another word.

See also: → pre-; → affix.

An → affix that is placed before a base to denote a modified meaning or make another word.

See also: → pre-; → affix.

Carefully chosen uniform exposure of a detector. For CCD this can be used to overcome the deferred charge phenomenon; in photography this helps bring dim images to a comfortably high density.

See also: → pre- + → flash.

Carefully chosen uniform exposure of a detector. For CCD this can be used to overcome the deferred charge phenomenon; in photography this helps bring dim images to a comfortably high density.

See also: → pre- + → flash.

1. Philosophy: To apprehend with or without conscious formulation or cognition of the perceived object; to interact in time and space with an object or event (Oxford Dictionary, lexico.com).
   

   2. (obsolete) To sieze.

Etymology (EN): From L. prehendere “to seize,” from prae- “before,” → pre-, + -hendere , from PIE root *ghend- “to seize, take,” root of Gk. khandanein “to hold, contain;” Lith. godetis “be eager;” Welsh gannu “to hold, contain;” Russian za-gadka “riddle;” Old Norse geta “to obtain, reach; to be able to;” E. get.

Etymology (PE): Nutidan, from nut-, from Yaghnobi nôta “to take,” from Sogd. niyât “to take, grasp,” from Proto-Ir. *ni-yāta-, from *iam- “to take, to hold;” cf. Av. yam- (yās-) “to hold, keep;” O.Pers. yas- “to strech, reach out;” Skt. yam- “to hold, restrain” (Cheung 2007).

1. Philosophy: To apprehend with or without conscious formulation or cognition of the perceived object; to interact in time and space with an object or event (Oxford Dictionary, lexico.com).
   

   2. (obsolete) To sieze.

Etymology (EN): From L. prehendere “to seize,” from prae- “before,” → pre-, + -hendere , from PIE root *ghend- “to seize, take,” root of Gk. khandanein “to hold, contain;” Lith. godetis “be eager;” Welsh gannu “to hold, contain;” Russian za-gadka “riddle;” Old Norse geta “to obtain, reach; to be able to;” E. get.

Etymology (PE): Nutidan, from nut-, from Yaghnobi nôta “to take,” from Sogd. niyât “to take, grasp,” from Proto-Ir. *ni-yāta-, from *iam- “to take, to hold;” cf. Av. yam- (yās-) “to hold, keep;” O.Pers. yas- “to strech, reach out;” Skt. yam- “to hold, restrain” (Cheung 2007).

1. Zoology Psychology: The action of grasping or seizing.
   

   2. Philosophy: An interaction of a subject with an event or entity which involves perception but not necessarily cognition (Oxford Dictionary, lexico.com).

See also: Verbal noun of → prehend.

1. Zoology Psychology: The action of grasping or seizing.
   

   2. Philosophy: An interaction of a subject with an event or entity which involves perception but not necessarily cognition (Oxford Dictionary, lexico.com).

See also: Verbal noun of → prehend.

Preceding and leading up to the main part, matter, or business; introductory; preparatory (Dictionary.com).

Etymology (EN): From Fr. préliminaire, from M.L. praeliminaris, from L. prae- “before,” → pre-,

• limen “threshold.”

Etymology (PE): Pišâstâni, literally “before the threshold,” from piš, → pre-, + âstâni, of or pertaining to âstân, → threshold.

Preceding and leading up to the main part, matter, or business; introductory; preparatory (Dictionary.com).

Etymology (EN): From Fr. préliminaire, from M.L. praeliminaris, from L. prae- “before,” → pre-,

• limen “threshold.”

Etymology (PE): Pišâstâni, literally “before the threshold,” from piš, → pre-, + âstâni, of or pertaining to âstân, → threshold.

Logic: An initial → proposition or statement that is known or assumed to be → true and on which a logical → argument is based.

Etymology (EN): From M.E. premiss, from O.Fr. premisse, from M.L. premissa (propositio) “(the proposition) set before,” feminine p.p. of L. praemittere “send or put before,” from prae “before,”
→ pre-, + mittere “to send,” → mission.

Etymology (PE): Pišpâyé, from piš-, → pre-, + pâyé, → base.

Logic: An initial → proposition or statement that is known or assumed to be → true and on which a logical → argument is based.

Etymology (EN): From M.E. premiss, from O.Fr. premisse, from M.L. premissa (propositio) “(the proposition) set before,” feminine p.p. of L. praemittere “send or put before,” from prae “before,”
→ pre-, + mittere “to send,” → mission.

Etymology (PE): Pišpâyé, from piš-, → pre-, + pâyé, → base.

In → particle physics, any of postulated “point-like” particles from which are composed → quarks and → leptons. In other words, preon models assume there is a more fundamental kind of particle than those so far known. Different preon models consider different numbers and different natures of the preons.

See also: Coined by Jogesh Pati and Abdus Salam in 1974, from → pre- + → -on.

In → particle physics, any of postulated “point-like” particles from which are composed → quarks and → leptons. In other words, preon models assume there is a more fundamental kind of particle than those so far known. Different preon models consider different numbers and different natures of the preons.

See also: Coined by Jogesh Pati and Abdus Salam in 1974, from → pre- + → -on.

A short-lived transition object between the → asymptotic giant branch (AGB) and → planetary nebula phases. See also
→ post-asymptotic giant branch star (post-AGB).

See also: → pre-; → planetary; → nebula. The more commonly used term, → protoplanetary nebula, is a misnomer and must be avoided. Indeed → protoplanetary is widely used to refer to disks around → pre-main sequence stars. Since the term → protoplanet is used to denote planets undergoing formation, the use of the term “protoplanetary nebula” to mean a completely different kind of object is an unfortunate choice (Sahai et al. 2005, ApJ 620, 948).

A short-lived transition object between the → asymptotic giant branch (AGB) and → planetary nebula phases. See also
→ post-asymptotic giant branch star (post-AGB).

See also: → pre-; → planetary; → nebula. The more commonly used term, → protoplanetary nebula, is a misnomer and must be avoided. Indeed → protoplanetary is widely used to refer to disks around → pre-main sequence stars. Since the term → protoplanet is used to denote planets undergoing formation, the use of the term “protoplanetary nebula” to mean a completely different kind of object is an unfortunate choice (Sahai et al. 2005, ApJ 620, 948).

A word used with a noun or pronoun to mark its relation with another word.

Etymology (EN): From L. praepositionem “a putting before,” from praepositus, p.p. of praeponere “put before,” from prae “before,” → pre-, + ponere “put, set, place,” → position.

Etymology (PE): Pišhel, from piš-, “before,” → pre-, + hel-, helidan, heštan “to place, put,” → leap.

A word used with a noun or pronoun to mark its relation with another word.

Etymology (EN): From L. praepositionem “a putting before,” from praepositus, p.p. of praeponere “put before,” from prae “before,” → pre-, + ponere “put, set, place,” → position.

Etymology (PE): Pišhel, from piš-, “before,” → pre-, + hel-, helidan, heštan “to place, put,” → leap.

An advance printing, usually of an article in a periodical.

See also: → pre-; → print.

An advance printing, usually of an article in a periodical.

See also: → pre-; → print.

Relating to a stage or time prior to the rise of modern science and to the application of the → scientific method.

See also: → pre-; → scientific.

Relating to a stage or time prior to the rise of modern science and to the application of the → scientific method.

See also: → pre-; → scientific.

1. To lay down, in writing or otherwise, as a rule or a course of action to be followed; appoint, ordain, or enjoin.
   

2. Medicine: To designate or order the use of a medicine, remedy, treatment, etc. (Dictionary.com).

See also: → pre-; + scribe, → inscribe.

1. To lay down, in writing or otherwise, as a rule or a course of action to be followed; appoint, ordain, or enjoin.
   

2. Medicine: To designate or order the use of a medicine, remedy, treatment, etc. (Dictionary.com).

See also: → pre-; + scribe, → inscribe.

1. An act of prescribing.
   

2. A direction, usually written, by the physician to the pharmacist for the preparation and use of a medicine or remedy. The medicine prescribed (Dictionary.com).

See also: Verbal noun of → prescribe; → -tion.

1. An act of prescribing.
   

2. A direction, usually written, by the physician to the pharmacist for the preparation and use of a medicine or remedy. The medicine prescribed (Dictionary.com).

See also: Verbal noun of → prescribe; → -tion.

1. That prescribes; giving directions or injunctions.
   

2. Depending on or arising from effective legal prescription, as a right or title established by a long unchallenged tenure (Dictionary.com).

See also: → prescribe; → -ive.

1. That prescribes; giving directions or injunctions.
   

2. Depending on or arising from effective legal prescription, as a right or title established by a long unchallenged tenure (Dictionary.com).

See also: → prescribe; → -ive.

The state or fact of being present.

See also: Noun from → present.

The state or fact of being present.

See also: Noun from → present.

1. Being, existing, or occurring at this time or now.
   

2. At this time; at hand; immediate.
   

3. Grammar: Noting an action or state occurring at the moment of speaking.

Etymology (EN): M.E., from O.Fr. present, from L. præsentem (nominative præsens) “present, immediate,” from pr.p. of præesse “to be before, to be at hand,” from præ- “before,” → pre-, + esse “to be;” cf. Pers. ast “is,” hastan, astan “to be;” O.P. ah- “to be,” astiy “is;” Av. ah- “to be,” astī “is;” Skt. as- “to be,” ásti “is;” Gk. esti “is;” PIE base es- “to be.”

Etymology (PE): Pišâst, on the model of L. præesse, as above, from piš, → pre-, + epenthetic -â- + ast “is,” variants hast, hi, has (Qâyen), isâ (Rašt), a (Aftar), heye (Kurd.); Av./O.Pers. ah- “to be,” Proto-Ir. *Hah- “to be,” → existence.
Bâšandé agent noun from budan “to be;”
→ condition.
Konuni “presently,” from konun, aknun “now, present,” from *hak-nun, from *hak-, cf. Av. hakat- “at once, immediately” + nū- “now” (Mid/Mod.Pers. nun “now, at present”); Av. nūrəm “now;” O.Pers.
nūram “now;” Skt. nú- “now, just, but,” nūnám “now, at present, indeed;” Gk. nun “now;” L. nu- “now” (in nu-dis “the day after tomorrow”); Goth. nu “now;” O.E. nu; E. now; PIE base *nu- “now.”

1. Being, existing, or occurring at this time or now.
   

2. At this time; at hand; immediate.
   

3. Grammar: Noting an action or state occurring at the moment of speaking.

Etymology (EN): M.E., from O.Fr. present, from L. præsentem (nominative præsens) “present, immediate,” from pr.p. of præesse “to be before, to be at hand,” from præ- “before,” → pre-, + esse “to be;” cf. Pers. ast “is,” hastan, astan “to be;” O.P. ah- “to be,” astiy “is;” Av. ah- “to be,” astī “is;” Skt. as- “to be,” ásti “is;” Gk. esti “is;” PIE base es- “to be.”

Etymology (PE): Pišâst, on the model of L. præesse, as above, from piš, → pre-, + epenthetic -â- + ast “is,” variants hast, hi, has (Qâyen), isâ (Rašt), a (Aftar), heye (Kurd.); Av./O.Pers. ah- “to be,” Proto-Ir. *Hah- “to be,” → existence.
Bâšandé agent noun from budan “to be;”
→ condition.
Konuni “presently,” from konun, aknun “now, present,” from *hak-nun, from *hak-, cf. Av. hakat- “at once, immediately” + nū- “now” (Mid/Mod.Pers. nun “now, at present”); Av. nūrəm “now;” O.Pers.
nūram “now;” Skt. nú- “now, just, but,” nūnám “now, at present, indeed;” Gk. nun “now;” L. nu- “now” (in nu-dis “the day after tomorrow”); Goth. nu “now;” O.E. nu; E. now; PIE base *nu- “now.”

Same as → present epoch, → today, → current cosmological epoch.

See also: → present; → day.

Same as → present epoch, → today, → current cosmological epoch.

See also: → present; → day.

Same as → present day, → today, → current cosmological epoch.

See also: → present; → epoch.

Same as → present day, → today, → current cosmological epoch.

See also: → present; → epoch.

A → participle that indicates an ongoing action or state in the present.

See also: → present; → participle.

A → participle that indicates an ongoing action or state in the present.

See also: → present; → participle.

The present number of stars on the → main sequence per unit logarithmic mass interval per square parsec. The PDMF is the basis for deriving the → initial mass function (IMF).
This mass function is not corrected for stellar evolution nor losses through stellar deaths.

See also: → present; → day; → mass; → function.

The present number of stars on the → main sequence per unit logarithmic mass interval per square parsec. The PDMF is the basis for deriving the → initial mass function (IMF).
This mass function is not corrected for stellar evolution nor losses through stellar deaths.

See also: → present; → day; → mass; → function.

To occupy the place of authority or control, as in an assembly or meeting; act as president or chairperson (Dictionary.com).

See also: → pre-; → reside.

To occupy the place of authority or control, as in an assembly or meeting; act as president or chairperson (Dictionary.com).

See also: → pre-; → reside.

1. The highest executive officer of a modern republic, as the Chief Executive of the United States (often initial capital letter).
   

2. An officer appointed or elected to preside over an organized body of persons (Dictionary.com).

Etymology (EN): → preside; → -ent.

Etymology (PE): Farneštgâr, from farnešt, present stem of farneštidan, → preside, + agent noun suffix -gâr, → -or, on the model of âmuzgâr “teacher.”

1. The highest executive officer of a modern republic, as the Chief Executive of the United States (often initial capital letter).
   

2. An officer appointed or elected to preside over an organized body of persons (Dictionary.com).

Etymology (EN): → preside; → -ent.

Etymology (PE): Farneštgâr, from farnešt, present stem of farneštidan, → preside, + agent noun suffix -gâr, → -or, on the model of âmuzgâr “teacher.”

Of or relating to an epoch earlier than the formation of the Sun.

See also: → pre-; → solar.

Of or relating to an epoch earlier than the formation of the Sun.

See also: → pre-; → solar.

A → refractory → nanoparticle embedded in → meteorites and → interplanetary dust particles whose → isotopic ratios suggest formation earlier than the Solar System.

See also: → presolar; → grain.

A → refractory → nanoparticle embedded in → meteorites and → interplanetary dust particles whose → isotopic ratios suggest formation earlier than the Solar System.

See also: → presolar; → grain.

A mathematical analysis, based on → self-similarity, used to predict the → mass function of spherically collapsing → dark matter halos. The formalism assumes that the fraction of mass in halos more massive than M is related to the fraction of the volume in which the smoothed initial density field is above some threshold δ_cρ, where ρ is the average density of the Universe, with the volume encompassing a mass larger than M. A variety of smoothing → window functions and thresholds have been argued, but the most common is a top-hat window
in real space and δ_c≅ 1.69. The Press-Schechter formalism provides a relatively good fit to the results of numerical simulations in cold dark matter theories.

See also: First described by William H. Press and Paul Schechter’s paper (1974, ApJ 187, 425); → formalism.

A mathematical analysis, based on → self-similarity, used to predict the → mass function of spherically collapsing → dark matter halos. The formalism assumes that the fraction of mass in halos more massive than M is related to the fraction of the volume in which the smoothed initial density field is above some threshold δ_cρ, where ρ is the average density of the Universe, with the volume encompassing a mass larger than M. A variety of smoothing → window functions and thresholds have been argued, but the most common is a top-hat window
in real space and δ_c≅ 1.69. The Press-Schechter formalism provides a relatively good fit to the results of numerical simulations in cold dark matter theories.

See also: First described by William H. Press and Paul Schechter’s paper (1974, ApJ 187, 425); → formalism.

The force per unit area.

Etymology (EN): M.E., from O.Fr. pressure, from L. pressura “action of pressing,” from pressus, p.p. of premere “to press, compress.”

Etymology (PE): Fešâr “squeezing, constriction, compression,” verb fešordan, fešârdan “to press, squeeze;” phonetic variants Lori xošâr, Aftari xešâr, Qazvini, Qomi xošâl; cf. Khotanese ssarr- “to exhilarate;” loaned in Arm. ôšarak, in Ar. afšaraj “juice.”

The force per unit area.

Etymology (EN): M.E., from O.Fr. pressure, from L. pressura “action of pressing,” from pressus, p.p. of premere “to press, compress.”

Etymology (PE): Fešâr “squeezing, constriction, compression,” verb fešordan, fešârdan “to press, squeeze;” phonetic variants Lori xošâr, Aftari xešâr, Qazvini, Qomi xošâl; cf. Khotanese ssarr- “to exhilarate;” loaned in Arm. ôšarak, in Ar. afšaraj “juice.”

A broadening of spectral lines caused mainly by the stellar atmospheric density and the surface gravity of the star. The line strength of a spectral line depends on the number of atoms in the star’s atmosphere capable of absorbing the wavelength in question. For a given temperature, the more atoms there are, the stronger and broader the spectral line appears. Denser stars with higher surface gravity will exhibit greater pressure broadening of spectral lines.

See also: → pressure; → broadening.

A broadening of spectral lines caused mainly by the stellar atmospheric density and the surface gravity of the star. The line strength of a spectral line depends on the number of atoms in the star’s atmosphere capable of absorbing the wavelength in question. For a given temperature, the more atoms there are, the stronger and broader the spectral line appears. Denser stars with higher surface gravity will exhibit greater pressure broadening of spectral lines.

See also: → pressure; → broadening.

The pressure difference between two adjacent regions of a fluid that results in
a force being exerted from the high pressure region toward the low pressure region.

See also: → pressure; → gradient.

The pressure difference between two adjacent regions of a fluid that results in
a force being exerted from the high pressure region toward the low pressure region.

See also: → pressure; → gradient.

A force resulting from → pressure gradient that is directed from high to low pressure.

See also: → pressure; → gradient; → force.

A force resulting from → pressure gradient that is directed from high to low pressure.

See also: → pressure; → gradient; → force.

A physical state of dense matter in which the electrostatic field of one atom should influence a neighboring atom and hence disturb atomic levels. In extreme case, such as white dwarfs, electron clouds practically rub and electrons are ionized off the parent atoms.

See also: → pressure; → ionization.

A physical state of dense matter in which the electrostatic field of one atom should influence a neighboring atom and hence disturb atomic levels. In extreme case, such as white dwarfs, electron clouds practically rub and electrons are ionized off the parent atoms.

See also: → pressure; → ionization.

Same as → p mode

See also: → pressure; → mode.

Same as → p mode

See also: → pressure; → mode.

A basic ingredient of the → mixing length theory that scales with the → mixing length. It is defined by the relation: H_P = -dr/dln P = -Pdr/dP , where r is the height and P the pressure. See also → scale height.

See also: → pressure; → scale; → height.

A basic ingredient of the → mixing length theory that scales with the → mixing length. It is defined by the relation: H_P = -dr/dln P = -Pdr/dP , where r is the height and P the pressure. See also → scale height.

See also: → pressure; → scale; → height.

Occurring before something else in time or order.

Etymology (EN): From L. praevius “leading the way,” from prae-,
→ pre- + via “way.”

Etymology (PE): Pišin, from piš “before,” → pre-.

Occurring before something else in time or order.

Etymology (EN): From L. praevius “leading the way,” from prae-,
→ pre- + via “way.”

Etymology (PE): Pišin, from piš “before,” → pre-.

Coming or occurring before something else; prior.

See also: → previous; → -ly.

Coming or occurring before something else; prior.

See also: → previous; → -ly.

A statement concerned with thermodynamic heat exchange, according to which bodies in → thermal equilibrium are simultaneously absorbing and emitting radiant energy. A body radiates in the same way whether other bodies are present or not. Also called Prevost’s theory of exchanges.

See also: Named after Pierre Prévost (1751-1839), a Swiss philosopher and physicist, who, in 1791, put forward the statement; → law; → exchange.

A statement concerned with thermodynamic heat exchange, according to which bodies in → thermal equilibrium are simultaneously absorbing and emitting radiant energy. A body radiates in the same way whether other bodies are present or not. Also called Prevost’s theory of exchanges.

See also: Named after Pierre Prévost (1751-1839), a Swiss philosopher and physicist, who, in 1791, put forward the statement; → law; → exchange.

1. To seize and devour prey, as an animal does.
   

   2. An animal hunted or seized for food, especially by a carnivorous animal (Dictionary.com).

Etymology (EN): M.E. preye, from O.Fr. preie, from L. praeda “booty, plunder, game hunted;” ultimately from prehendere “to grasp, seize.”

Etymology (PE): 1) Cavidan, related to Khotanese cev- “to get, seize,” Ossetic cævyn, cavd “to hit, to strike,” Pers. câpidan “to plunder,” cafsidan, caspidan “to stick; to plunder;” Proto-Ir. *cap- “to seize.”

2. Cavâk, from cav- present stem of cavidan, as above,

• -âk suffix denoting object of an action.

1. To seize and devour prey, as an animal does.
   

   2. An animal hunted or seized for food, especially by a carnivorous animal (Dictionary.com).

Etymology (EN): M.E. preye, from O.Fr. preie, from L. praeda “booty, plunder, game hunted;” ultimately from prehendere “to grasp, seize.”

Etymology (PE): 1) Cavidan, related to Khotanese cev- “to get, seize,” Ossetic cævyn, cavd “to hit, to strike,” Pers. câpidan “to plunder,” cafsidan, caspidan “to stick; to plunder;” Proto-Ir. *cap- “to seize.”

2. Cavâk, from cav- present stem of cavidan, as above,

• -âk suffix denoting object of an action.

An animal that is hunted and killed by a → predator as food.

See also: → prey; → animal.

An animal that is hunted and killed by a → predator as food.

See also: → prey; → animal.

The concentric colored rings formed by an electrical → spark when a → discharge takes place on a metallic plate.

See also: Joseph Priestley (1733-1804), English chemist, author, and clergyman; → ring.

The concentric colored rings formed by an electrical → spark when a → discharge takes place on a metallic plate.

See also: Joseph Priestley (1733-1804), English chemist, author, and clergyman; → ring.

1. First or highest in rank or importance; chief; principal.
   

2. Abbreviation for → primary body, → primary star, or → primary mirror.

Etymology (EN): M.E., from L. primarius “of the first rank, principal,” from primus “first.”

Etymology (PE): Naxostân, from
naxost, from Mid.Pers. naxust “the first,” Parthian Mid.Pers. nxwšt, from naxu, Manichean Parthian nwx “beginning” + -ist superlative suffix, Av. -išta-, cf. Skt. -istha-, Gk. -istos, O.H.G. -isto, -osto, O.E. -st, -est, -ost.

1. First or highest in rank or importance; chief; principal.
   

2. Abbreviation for → primary body, → primary star, or → primary mirror.

Etymology (EN): M.E., from L. primarius “of the first rank, principal,” from primus “first.”

Etymology (PE): Naxostân, from
naxost, from Mid.Pers. naxust “the first,” Parthian Mid.Pers. nxwšt, from naxu, Manichean Parthian nwx “beginning” + -ist superlative suffix, Av. -išta-, cf. Skt. -istha-, Gk. -istos, O.H.G. -isto, -osto, O.E. -st, -est, -ost.

The body that is being orbited; such as the → Sun in the → solar system. As regards → multiple star systems, the most massive, or → primary star. See also: → secondary body.

See also: → primary; → body.

The body that is being orbited; such as the → Sun in the → solar system. As regards → multiple star systems, the most massive, or → primary star. See also: → secondary body.

See also: → primary; → body.

A → cell in which the electrochemical action producing the current is not normally reversible. Such a cell cannot be recharged by an electric current. → secondary cell.

See also: → primary; → cell.

A → cell in which the electrochemical action producing the current is not normally reversible. Such a cell cannot be recharged by an electric current. → secondary cell.

See also: → primary; → cell.

The → cosmic rays which arrive on the Earth’s → atmosphere from the outer space. The primary cosmic rays are very high energy → protons and to a lesser extent heavier nuclei which rain upon the Earth from all diretions in the outer space. They contain about 90% protons, 7% → alpha particles and about 1% still heavier nuclei of amost all the atoms from Li to Ni ( → mass number< 60). See also: → secondary cosmic rays.

See also: → primary; → cosmic; → ray.

The → cosmic rays which arrive on the Earth’s → atmosphere from the outer space. The primary cosmic rays are very high energy → protons and to a lesser extent heavier nuclei which rain upon the Earth from all diretions in the outer space. They contain about 90% protons, 7% → alpha particles and about 1% still heavier nuclei of amost all the atoms from Li to Ni ( → mass number< 60). See also: → secondary cosmic rays.

See also: → primary; → cosmic; → ray.

Of a transiting → exoplanet, the event and the interval of time during which the planet passes in front of its host star. The planet occults a portion of the stellar disk, and a fraction of light from the star is seen after traversal through the atmosphere around the planet’s limb. → secondary eclipse.

See also: → primary; → eclipse.

Of a transiting → exoplanet, the event and the interval of time during which the planet passes in front of its host star. The planet occults a portion of the stellar disk, and a fraction of light from the star is seen after traversal through the atmosphere around the planet’s limb. → secondary eclipse.

See also: → primary; → eclipse.

In a → reflecting telescope, the first mirror that collects the light and focuses it to the → focal plane.

See also: → primary; → mirror.

In a → reflecting telescope, the first mirror that collects the light and focuses it to the → focal plane.

See also: → primary; → mirror.

The main rainbow that forms between about 40° and 42° from the → antisolar point (or about 50° from the → antisolar point), as viewed by the observer. The light path involves → refraction and a → single  → reflection inside the water → droplet. If the drops are large, 1 millimeter or more in diameter, red, green, and violet are bright but there is little blue.

As the droplets get smaller, red weakens.

Rainbows are not seen in midday since the whole 42° circle is below the horizon at most latitudes. So rainbows tend to be seen most in the later afternoon when a thundershower has passed and the Sun is illuminating from the west.

See also: → primary; → rainbow.

The main rainbow that forms between about 40° and 42° from the → antisolar point (or about 50° from the → antisolar point), as viewed by the observer. The light path involves → refraction and a → single  → reflection inside the water → droplet. If the drops are large, 1 millimeter or more in diameter, red, green, and violet are bright but there is little blue.

As the droplets get smaller, red weakens.

Rainbows are not seen in midday since the whole 42° circle is below the horizon at most latitudes. So rainbows tend to be seen most in the later afternoon when a thundershower has passed and the Sun is illuminating from the west.

See also: → primary; → rainbow.

In a → multiple star system, the most massive → component. In other words, the star nearest to the system’s → center of garvity.

See also: → primary; → star .

In a → multiple star system, the most massive → component. In other words, the star nearest to the system’s → center of garvity.

See also: → primary; → star .

1. Of the first importance; of the highest rank.
   

2. Same as → prime number.

Etymology (EN): M.E., from L. primarius “of the first rank, principal,” from primus “first.”

Etymology (PE): Naxost, naxostin, naxosti, from
Mid.Pers. naxust “the first,” Parthian Mid.Pers. nxwšt, from naxu, Manichean Parthian nwx “beginning” + -ist superlative suffix, Av. -išta-, cf. Skt. -istha-, Gk. -istos, O.H.G. -isto, -osto, O.E. -st, -est, -ost.

1. Of the first importance; of the highest rank.
   

2. Same as → prime number.

Etymology (EN): M.E., from L. primarius “of the first rank, principal,” from primus “first.”

Etymology (PE): Naxost, naxostin, naxosti, from
Mid.Pers. naxust “the first,” Parthian Mid.Pers. nxwšt, from naxu, Manichean Parthian nwx “beginning” + -ist superlative suffix, Av. -išta-, cf. Skt. -istha-, Gk. -istos, O.H.G. -isto, -osto, O.E. -st, -est, -ost.

The focal point of a large primary reflecting mirror. This focus actually falls at a point just within the upper structure of the telescope and provides a large field of view.

See also: → primary; → focus.

The focal point of a large primary reflecting mirror. This focus actually falls at a point just within the upper structure of the telescope and provides a large field of view.

See also: → primary; → focus.

The meridian at which longitude is defined to be 0°. The meridian running through Greenwich.

See also: → primary; → meridian.

The meridian at which longitude is defined to be 0°. The meridian running through Greenwich.

See also: → primary; → meridian.

A number which is divisible by no whole number other than itself and one.

See also: → prime; → number.

A number which is divisible by no whole number other than itself and one.

See also: → prime; → number.

The great circle through the observer’s zenith that
intersects the horizon at the west and east points. → vertical circle.

See also: → primary; → vertical.

The great circle through the observer’s zenith that
intersects the horizon at the west and east points. → vertical circle.

See also: → primary; → vertical.

Lemaître’s (1931) name for the early dense Universe, which later became known as the → Big Bang theory.

See also: From L. primaevus “early in life,” from primus “first,” → prime, + aevum “an age,” + → -al; → atom.

Lemaître’s (1931) name for the early dense Universe, which later became known as the → Big Bang theory.

See also: From L. primaevus “early in life,” from primus “first,” → prime, + aevum “an age,” + → -al; → atom.

Pertaining to or existing at or from the very beginning.

Etymology (EN): From L.L. primordialis “first of all, original,” from L. primordium “the beginning,” from primus “first” + stem of ordiri “to begin.”

Etymology (PE): Bonâqâzin, from bon “basis; root; foundation; bottom” (Mid.Pers. bun “root; foundation; beginning,” Av. būna- “base, depth,” cf. Skt. bundha-, budhná- “base, bottom,” Pali bunda- “root of tree”)

• âqâzin “pertaining to the beginning,” from âqâz “beginning” (Proto-Iranian *āgāza-, from prefix ā-
• *gāz- “to take, receive,” cf. Sogdian āγāz “beginning, start,” pcγz “reception, taking”).

Pertaining to or existing at or from the very beginning.

Etymology (EN): From L.L. primordialis “first of all, original,” from L. primordium “the beginning,” from primus “first” + stem of ordiri “to begin.”

Etymology (PE): Bonâqâzin, from bon “basis; root; foundation; bottom” (Mid.Pers. bun “root; foundation; beginning,” Av. būna- “base, depth,” cf. Skt. bundha-, budhná- “base, bottom,” Pali bunda- “root of tree”)

• âqâzin “pertaining to the beginning,” from âqâz “beginning” (Proto-Iranian *āgāza-, from prefix ā-
• *gāz- “to take, receive,” cf. Sogdian āγāz “beginning, start,” pcγz “reception, taking”).

The relative amount of a light element (e.g. deuterium, lithium, helium) synthesized in the early Universe.

See also: → primordial; → abundance.

The relative amount of a light element (e.g. deuterium, lithium, helium) synthesized in the early Universe.

See also: → primordial; → abundance.

A black hole formed following the Big Bang event due to incredibly violent turbulence that squeezed concentrations of matter to high densities. These black holes, first suggested by
Stephen Hawking, are expected to have a mass comparable to that of a mountain and a size as small as an atom. Same as → mini black hole.

See also: → primordial; → black hole.

A black hole formed following the Big Bang event due to incredibly violent turbulence that squeezed concentrations of matter to high densities. These black holes, first suggested by
Stephen Hawking, are expected to have a mass comparable to that of a mountain and a size as small as an atom. Same as → mini black hole.

See also: → primordial; → black hole.

In cosmological models, the phenomenon that is supposed to seed the → cosmic microwave background anisotropies and the structure formation of the Universe.

See also: → primordial; → curvature; → perturbation.

In cosmological models, the phenomenon that is supposed to seed the → cosmic microwave background anisotropies and the structure formation of the Universe.

See also: → primordial; → curvature; → perturbation.

A high redshift, metal-deficient galaxy that formed very early in the history of the Universe.

See also: → primordial; → galaxy.

A high redshift, metal-deficient galaxy that formed very early in the history of the Universe.

See also: → primordial; → galaxy.

The helium element created in the → early Universe, around 3 minutes after the → Big Bang, when the temperature dropped to 10⁹ degrees; in contrast to the helium being synthesized in stars.

Based on observations of helium → emission lines in → H II regions of metal-poor dwarf galaxies (→ metal-deficient galaxy), the primordial ⁴He → chemical abundance (by mass) is estimated to be Y_P = 0.24672 ± 0.00017. Moreover, using observations of a near-pristine → intergalactic cloud, a value of
0.250 ^+0.033_-0.025 has been reached
(Cooke & Fumagalli, 2018, Nature Astronomy, 2, 657). The theoretical He abundance predicted by → Big Bang nucleosynthesis is
0.24709 ± 0.00017 (Pitrou et al., 2018, arXiv:1801.08023).

See also: → primordial; → helium.

The helium element created in the → early Universe, around 3 minutes after the → Big Bang, when the temperature dropped to 10⁹ degrees; in contrast to the helium being synthesized in stars.

Based on observations of helium → emission lines in → H II regions of metal-poor dwarf galaxies (→ metal-deficient galaxy), the primordial ⁴He → chemical abundance (by mass) is estimated to be Y_P = 0.24672 ± 0.00017. Moreover, using observations of a near-pristine → intergalactic cloud, a value of
0.250 ^+0.033_-0.025 has been reached
(Cooke & Fumagalli, 2018, Nature Astronomy, 2, 657). The theoretical He abundance predicted by → Big Bang nucleosynthesis is
0.24709 ± 0.00017 (Pitrou et al., 2018, arXiv:1801.08023).

See also: → primordial; → helium.

The formation of → chemical elements in the → early Universe, between about 0.01 seconds and 3 minutes after the → Big Bang, when the nuclei of primordial matter collided and fused with one another. Most of the → helium in the → Universe was created by this process. Same as → Big Bang nucleosynthesis

See also: → primordial; → nucleosynthesis.

The formation of → chemical elements in the → early Universe, between about 0.01 seconds and 3 minutes after the → Big Bang, when the nuclei of primordial matter collided and fused with one another. Most of the → helium in the → Universe was created by this process. Same as → Big Bang nucleosynthesis

See also: → primordial; → nucleosynthesis.

First or highest in rank, importance, value, etc. See also → main.

Etymology (EN): M.E., from O.Fr. principal, from L. principalis “first in importance,” from princeps “first, chief, prince,” literally “that takes first,” from primus “first” + root of capere “to take.”

Etymology (PE): Farin literally “foremost,” from far-, Mid.Pers. fra-; O.Pers. fra- “forward, forth;” Av. frā “forth,” pouruua- “first;” cf. Skt. pūrva- “first,” pra- “before, formerly;” Gk. pro; L. pro; O.E. fyrst “foremost,” superlative of fore, E. fore + -in superlative suffix.

First or highest in rank, importance, value, etc. See also → main.

Etymology (EN): M.E., from O.Fr. principal, from L. principalis “first in importance,” from princeps “first, chief, prince,” literally “that takes first,” from primus “first” + root of capere “to take.”

Etymology (PE): Farin literally “foremost,” from far-, Mid.Pers. fra-; O.Pers. fra- “forward, forth;” Av. frā “forth,” pouruua- “first;” cf. Skt. pūrva- “first,” pra- “before, formerly;” Gk. pro; L. pro; O.E. fyrst “foremost,” superlative of fore, E. fore + -in superlative suffix.

1. Optics: Any imaginary line passing through the center of curvature of a → spherical mirror or → lens and the corresponding geometrical center.

Principal axis is perpendicular to the mirror or lens at the pole. Rays of light parallel to the principal axis of a → concave mirror

will appear to converge on a point in front of the mirror somewhere between the mirror’s pole and its center of curvature. Same as → optical axis.

2. Mechanics: One of three mutually perpendicular axes of an object about which the → moment of inertia is maximum or minimum.

More specifically, an object has an infinite number of moments of inertia. If an object is not symmetrical about all planes through its → center of mass, then there will be one → axis of rotation about which the moment of inertia is largest, and there will be one axis of rotation about which the moment of inertia is smallest. These two axes will always be perpendicular to each other and are the principal axes of the object. The third principal axis of an object is the axis perpendicular to these two axes.

In general the → angular momentum (L) of a body spinning about a point O is not in the same direction as the axis of rotation, or that of the → angular velocity angular velocity (ω); that is L is not parallel to ω. For certain bodies, however, there can be certain axes for which L and ω are parallel. In that case L = Iω, where I is the moment of inertia about the axis in question.

In a symmetric rigid body, the axes of symmetry coincide with the principal axes of the moment of inertia

See also: → principal; → axis.

1. Optics: Any imaginary line passing through the center of curvature of a → spherical mirror or → lens and the corresponding geometrical center.

Principal axis is perpendicular to the mirror or lens at the pole. Rays of light parallel to the principal axis of a → concave mirror

will appear to converge on a point in front of the mirror somewhere between the mirror’s pole and its center of curvature. Same as → optical axis.

2. Mechanics: One of three mutually perpendicular axes of an object about which the → moment of inertia is maximum or minimum.

More specifically, an object has an infinite number of moments of inertia. If an object is not symmetrical about all planes through its → center of mass, then there will be one → axis of rotation about which the moment of inertia is largest, and there will be one axis of rotation about which the moment of inertia is smallest. These two axes will always be perpendicular to each other and are the principal axes of the object. The third principal axis of an object is the axis perpendicular to these two axes.

In general the → angular momentum (L) of a body spinning about a point O is not in the same direction as the axis of rotation, or that of the → angular velocity angular velocity (ω); that is L is not parallel to ω. For certain bodies, however, there can be certain axes for which L and ω are parallel. In that case L = Iω, where I is the moment of inertia about the axis in question.

In a symmetric rigid body, the axes of symmetry coincide with the principal axes of the moment of inertia

See also: → principal; → axis.

In atomic physics, the first of a set of quantum numbers which describe an atomic orbital. Symbolized as n, it characterizes the size and energy of an orbital.

See also: → principal; → quantum;
→ number.

In atomic physics, the first of a set of quantum numbers which describe an atomic orbital. Symbolized as n, it characterizes the size and energy of an orbital.

See also: → principal; → quantum;
→ number.

A fundamental, primary assumption, or general law from which others are derived.

Etymology (EN): From M.E., from O.Fr. principe, from L. principium “a beginning, first part,” from princeps “first, chief, prince,” literally “that takes first,” from primus “first” + root of capere “to take.”

Etymology (PE): Parvaz “origin, root, stock” (as used in particular by Ferdowsi); cf. Av. fra-vāza- “drawing from; leading onward,” from Av. fra-, frā- “before; forward, forth” (fratəma- “first, front,” pouruua- “first,” fra-cara- “preceding;”
O.Pers. fra- “forward, forth;” Mid.Pers. fra-;
cf. Skt. pra- “before, formerly,” prathama- “earliest, initial,” pūrva- “first;” Gk. pro; L. pro; O.E. fyrst “foremost,” superlative of fore)

• vaz- “to draw, guide; bring; possess; fly; float,” vazaiti “guides, leads”
  (cf. Skt. vah- “to carry, drive, convey,” vahati “carries,”
  pravaha- “bearing along, carrying,” pravāha- “running water, stream, river;” L. vehere “to carry;” O.E. wegan “to carry;” O.N. vegr; O.H.G. weg “way,” wegan “to move,” wagan “cart;” M.Du. wagen “wagon;” PIE base *wegh- “to drive;” see also → flight).

A fundamental, primary assumption, or general law from which others are derived.

Etymology (EN): From M.E., from O.Fr. principe, from L. principium “a beginning, first part,” from princeps “first, chief, prince,” literally “that takes first,” from primus “first” + root of capere “to take.”

Etymology (PE): Parvaz “origin, root, stock” (as used in particular by Ferdowsi); cf. Av. fra-vāza- “drawing from; leading onward,” from Av. fra-, frā- “before; forward, forth” (fratəma- “first, front,” pouruua- “first,” fra-cara- “preceding;”
O.Pers. fra- “forward, forth;” Mid.Pers. fra-;
cf. Skt. pra- “before, formerly,” prathama- “earliest, initial,” pūrva- “first;” Gk. pro; L. pro; O.E. fyrst “foremost,” superlative of fore)

• vaz- “to draw, guide; bring; possess; fly; float,” vazaiti “guides, leads”
  (cf. Skt. vah- “to carry, drive, convey,” vahati “carries,”
  pravaha- “bearing along, carrying,” pravāha- “running water, stream, river;” L. vehere “to carry;” O.E. wegan “to carry;” O.N. vegr; O.H.G. weg “way,” wegan “to move,” wagan “cart;” M.Du. wagen “wagon;” PIE base *wegh- “to drive;” see also → flight).

Newton’s third law of motion, which states that for every action there must be an equal and opposite reaction.

See also: → principle; → action; → reaction.

Newton’s third law of motion, which states that for every action there must be an equal and opposite reaction.

See also: → principle; → action; → reaction.

The second postulate in Einstein’s theory of → special relativity whereby the → velocity of light in → vacuum has the same absolute value in all → inertial reference frames irrespective of the direction and speed of propagation of the light source. It should be emphasized that this constancy of the speed of light holds among → reference frames moving uniformly with respect to each other. An observer accelerated with respect to a light source will measure a speed of light that is smaller than the speed of light measured in a → rest frame. See also → principle of relativity.

See also: → principle; constancy, noun related to → constant.

The second postulate in Einstein’s theory of → special relativity whereby the → velocity of light in → vacuum has the same absolute value in all → inertial reference frames irrespective of the direction and speed of propagation of the light source. It should be emphasized that this constancy of the speed of light holds among → reference frames moving uniformly with respect to each other. An observer accelerated with respect to a light source will measure a speed of light that is smaller than the speed of light measured in a → rest frame. See also → principle of relativity.

See also: → principle; constancy, noun related to → constant.

In special relativity, the principle that the laws of physics take the same mathematical form in all inertial frames of reference.

See also: → principle; → covariance.

In special relativity, the principle that the laws of physics take the same mathematical form in all inertial frames of reference.

See also: → principle; → covariance.

In → general relativity the principle
which states that in the immediate proximity of an → accelerating system the acceleration is physically equivalent to → gravitational force.
This principle also implies the equivalence of → gravitational mass and → inertial mass. Same as the → equivalence principle. See also → Einstein’s elevator.

See also: → principle; → equivalence.

In → general relativity the principle
which states that in the immediate proximity of an → accelerating system the acceleration is physically equivalent to → gravitational force.
This principle also implies the equivalence of → gravitational mass and → inertial mass. Same as the → equivalence principle. See also → Einstein’s elevator.

See also: → principle; → equivalence.

The second principle of → formal logic introduced in Aristotle’s theory of the → syllogism: A
statement is either → true or → false. In other words, two → contradictory → propositions cannot both be true. The truth of one implies the falsehood of the other. Also called law of excluded middle and → principle of excluded third.

See also: → principle; → exclude; → middle.

The second principle of → formal logic introduced in Aristotle’s theory of the → syllogism: A
statement is either → true or → false. In other words, two → contradictory → propositions cannot both be true. The truth of one implies the falsehood of the other. Also called law of excluded middle and → principle of excluded third.

See also: → principle; → exclude; → middle.

Same as → principle of excluded middle.

See also: → principle; → exclude; → third.

Same as → principle of excluded middle.

See also: → principle; → exclude; → third.

The first principle of → formal logic introduced in Aristotle’s
theory of the → syllogism: If a statement is true then it is true. Also called → law of identity.

See also: → principle; → identity.

The first principle of → formal logic introduced in Aristotle’s
theory of the → syllogism: If a statement is true then it is true. Also called → law of identity.

See also: → principle; → identity.

The principle that, for a system whose total mechanical energy is conserved, the path to be taken for the system from one configuration to another is the one whose action has the least value relative to all other possible paths and from the same configurations. Also called Maupertuis’ principle, least-action principle.

See also: → principle; → least; → action.

The principle that, for a system whose total mechanical energy is conserved, the path to be taken for the system from one configuration to another is the one whose action has the least value relative to all other possible paths and from the same configurations. Also called Maupertuis’ principle, least-action principle.

See also: → principle; → least; → action.

The third principle of → formal logic introduced in Aristotle’s
theory of the → syllogism: No statement can be both → true and → false at the same time. Also called → law of non-contradiction.

See also: → principle; → non-; → contradiction.

The third principle of → formal logic introduced in Aristotle’s
theory of the → syllogism: No statement can be both → true and → false at the same time. Also called → law of non-contradiction.

See also: → principle; → non-; → contradiction.

One consequence of the theory of → special relativity, according to which no two events separated by a distance greater than their separation in time multiplied by the → speed of light may have a → causal influence on each other. Violation of this principle leads to → paradoxes, such as that of an → effect preceding its → cause.

See also: → principle; → relativistic; → causality.

One consequence of the theory of → special relativity, according to which no two events separated by a distance greater than their separation in time multiplied by the → speed of light may have a → causal influence on each other. Violation of this principle leads to → paradoxes, such as that of an → effect preceding its → cause.

See also: → principle; → relativistic; → causality.

The first postulate in Einstein’s theory of → special relativity whereby all the laws of physics are the same in every → inertial reference frame. In other words, no physical measurement can distinguish one inertial reference frame from another. See also → principle of constancy.

See also: → principle;
→ relativity.

The first postulate in Einstein’s theory of → special relativity whereby all the laws of physics are the same in every → inertial reference frame. In other words, no physical measurement can distinguish one inertial reference frame from another. See also → principle of constancy.

See also: → principle;
→ relativity.

1a) The state of being printed.

1b) Printed lettering, especially with reference to character, style, or size.

1c) Printed material; a printed publication, as a newspaper or magazine.

2a) To produce (a text, picture, etc.) by applying inked types, plates, blocks, or the like, to paper or other material either by direct pressure or indirectly by offsetting an image onto an intermediate roller.

2b) To reproduce (a design or pattern) by engraving on a plate or block.

2c) To form a design or pattern upon, as by stamping with an engraved plate or block.

2d) To cause (a manuscript, text, etc.) to be published in print (Dictionary.com).

Etymology (EN): M.E. prent(e), print(e), prient(e), from OF priente “impression,” noun use of feminine p.p. of preindre “to press,” from L. premere “to press, hold fast.”

Etymology (PE): Câp “press,” loan from Indo-Aryan languages chapa, chháp, chāp “seal, stamp, impression.”

1a) The state of being printed.

1b) Printed lettering, especially with reference to character, style, or size.

1c) Printed material; a printed publication, as a newspaper or magazine.

2a) To produce (a text, picture, etc.) by applying inked types, plates, blocks, or the like, to paper or other material either by direct pressure or indirectly by offsetting an image onto an intermediate roller.

2b) To reproduce (a design or pattern) by engraving on a plate or block.

2c) To form a design or pattern upon, as by stamping with an engraved plate or block.

2d) To cause (a manuscript, text, etc.) to be published in print (Dictionary.com).

Etymology (EN): M.E. prent(e), print(e), prient(e), from OF priente “impression,” noun use of feminine p.p. of preindre “to press,” from L. premere “to press, hold fast.”

Etymology (PE): Câp “press,” loan from Indo-Aryan languages chapa, chháp, chāp “seal, stamp, impression.”

1. A person or thing that prints, especially a person whose occupation is printing.
   

2. Computers: An output device that produces a paper copy of alphanumeric or graphic data (Dictionary.com).

See also: → print; → -er.

1. A person or thing that prints, especially a person whose occupation is printing.
   

2. Computers: An output device that produces a paper copy of alphanumeric or graphic data (Dictionary.com).

See also: → print; → -er.

A font used for printing. See also → screen font.

See also: → printer; → font.

A font used for printing. See also → screen font.

See also: → printer; → font.

1. Preceding in time or in order; earlier or former; previous.
   

2. Preceding in importance or privilege.

Etymology (EN): O.E., from M.L. prior “former, previous, first, superior,” comparative of O.L. pri “before,” from PIE *prai-, *prei-, from root *per- “forward, through,” → pro-.

Etymology (PE): Parin, from pra-, fra- “before, forward, forth,” cognate with Gk. and L. → pro-.

1. Preceding in time or in order; earlier or former; previous.
   

2. Preceding in importance or privilege.

Etymology (EN): O.E., from M.L. prior “former, previous, first, superior,” comparative of O.L. pri “before,” from PIE *prai-, *prei-, from root *per- “forward, through,” → pro-.

Etymology (PE): Parin, from pra-, fra- “before, forward, forth,” cognate with Gk. and L. → pro-.

The condition or quality of being earlier in time or occurrence, or being regarded as more important.

See also: → prior; → -ity.

The condition or quality of being earlier in time or occurrence, or being regarded as more important.

See also: → prior; → -ity.

Optics:
A transparent solid body, having at least two polished plane faces inclined relative to each other, from which light is reflected or through which light is refracted.
Geometry: A solid having two faces lying in parallel planes and with the other faces parallelograms.

Etymology (EN): L.L. prisma, from Gk. prisma, literally “something sawed,” from prizein “to saw.”

Etymology (PE): Manšur, etymology not clear, may be related to Ar. mawšur “prism,” of unknown origin.

Optics:
A transparent solid body, having at least two polished plane faces inclined relative to each other, from which light is reflected or through which light is refracted.
Geometry: A solid having two faces lying in parallel planes and with the other faces parallelograms.

Etymology (EN): L.L. prisma, from Gk. prisma, literally “something sawed,” from prizein “to saw.”

Etymology (PE): Manšur, etymology not clear, may be related to Ar. mawšur “prism,” of unknown origin.

The angle between the faces on which light is incident and from which it emerges.

See also: → prism; → angle.

The angle between the faces on which light is incident and from which it emerges.

See also: → prism; → angle.

An optical device consisting of a pair of small telescopes mounted side by side, each telescope having two prisms between the eyepiece and objective for erecting the image.

See also: → prism; → binoculars.

An optical device consisting of a pair of small telescopes mounted side by side, each telescope having two prisms between the eyepiece and objective for erecting the image.

See also: → prism; → binoculars.

An ocular equipped with a prism that forms an upright image in an astronomical telescope.

See also: → prism; → ocular.

An ocular equipped with a prism that forms an upright image in an astronomical telescope.

See also: → prism; → ocular.

An instrument used to determine the precise timing of a star’s passage across a vertical circle.
It is used for making precise determinations of the positions of stars and planets, and can be used inversely to determine the latitude and longitude of the observer, assuming the star positions are accurately known. It consists of an accurate prism, a small pool of mercury to serve as an artificial horizon.
The most notable example of this type of instrument is that of → Danjon astrolabe.

See also: Adj. of → prism + → astrolabe.

An instrument used to determine the precise timing of a star’s passage across a vertical circle.
It is used for making precise determinations of the positions of stars and planets, and can be used inversely to determine the latitude and longitude of the observer, assuming the star positions are accurately known. It consists of an accurate prism, a small pool of mercury to serve as an artificial horizon.
The most notable example of this type of instrument is that of → Danjon astrolabe.

See also: Adj. of → prism + → astrolabe.

The spectrum formed by a dispersing prism or a dispersing prism system.

See also: Adj. of → prism + → spectrum.

The spectrum formed by a dispersing prism or a dispersing prism system.

See also: Adj. of → prism + → spectrum.

The state of being private.

See also: Noun from → private.

The state of being private.

See also: Noun from → private.

Pertaining to or affecting a particular person or a small group of persons; individual; → personal (Dictionary.com).

Etymology (EN): L. privatus “set apart, peculiar, personal,” used in contrast to publicus, p.p. of privare “to separate, deprive, to rob” from privus “one’s own, individual.”

Etymology (PE): Vâvan, literally “separated, not bound,” from vâ- separation prefix,
→ de-, + van, contraction of vand, band, from vastan, bastan “to bind, fasten, close,” → band.

Pertaining to or affecting a particular person or a small group of persons; individual; → personal (Dictionary.com).

Etymology (EN): L. privatus “set apart, peculiar, personal,” used in contrast to publicus, p.p. of privare “to separate, deprive, to rob” from privus “one’s own, individual.”

Etymology (PE): Vâvan, literally “separated, not bound,” from vâ- separation prefix,
→ de-, + van, contraction of vand, band, from vastan, bastan “to bind, fasten, close,” → band.

The transfer from public to private ownership.

See also: → private; → -tion.

The transfer from public to private ownership.

See also: → private; → -tion.

To transfer from public to private ownership and control.

See also: → private; → -ize.

To transfer from public to private ownership and control.

See also: → private; → -ize.

A special right, advantage, or immunity granted or available only to a particular person or group (OxfordDictionaries.com).

Etymology (EN): M.E., from O.Fr. privilege “right, priority, privilege” and directly from L. privilegium “law applying to one person, bill of law in favor of or against an individual,” from privus “individual,” → private.

Etymology (PE): Fardâré, from far- intensive prefix “much, abundant; elegantly,” → perfect, + dâr present stem of dâštan “to have, possess,” → property, + noun/relation suffix -é.

A special right, advantage, or immunity granted or available only to a particular person or group (OxfordDictionaries.com).

Etymology (EN): M.E., from O.Fr. privilege “right, priority, privilege” and directly from L. privilegium “law applying to one person, bill of law in favor of or against an individual,” from privus “individual,” → private.

Etymology (PE): Fardâré, from far- intensive prefix “much, abundant; elegantly,” → perfect, + dâr present stem of dâštan “to have, possess,” → property, + noun/relation suffix -é.

Having special rights, advantages, or immunities.

See also: Adjective from → privilege.

Having special rights, advantages, or immunities.

See also: Adjective from → privilege.

A prefix of priority in space or time having especially a meaning of advancing or projecting forward or outward.

Etymology (EN): From L. pro “in favor of, in place of, before, for,” also in some cases from cognate Gk. pro “before, in front of,” both from PIE base *por- “forward, through;” cf. Pers. farâ-, as below; Gk. para- “from beside, against, beyond;” Goth. faura “before,” O.E. fore “before, for, on account of.”

Etymology (PE): Farâ- “forward, along; above, upon, over; before, foremost, opposing, facing,” variant far- intensive prefix “much, abundant; elegantly,” from Mid.Pers. fra-; O.Pers. fra- “forward, forth;” Av. frā, fərā-, fra- “forward, forth; before; excessive” (fratəma- “first, front,” pouruua- “first,” fra-cara- “preceding”);
cf. Skt. prá- “before; forward, in fron,” prathama- “earliest, initial,” pūrva- “first;” Gk. pro; L. pro, as above.

A prefix of priority in space or time having especially a meaning of advancing or projecting forward or outward.

Etymology (EN): From L. pro “in favor of, in place of, before, for,” also in some cases from cognate Gk. pro “before, in front of,” both from PIE base *por- “forward, through;” cf. Pers. farâ-, as below; Gk. para- “from beside, against, beyond;” Goth. faura “before,” O.E. fore “before, for, on account of.”

Etymology (PE): Farâ- “forward, along; above, upon, over; before, foremost, opposing, facing,” variant far- intensive prefix “much, abundant; elegantly,” from Mid.Pers. fra-; O.Pers. fra- “forward, forth;” Av. frā, fərā-, fra- “forward, forth; before; excessive” (fratəma- “first, front,” pouruua- “first,” fra-cara- “preceding”);
cf. Skt. prá- “before; forward, in fron,” prathama- “earliest, initial,” pūrva- “first;” Gk. pro; L. pro, as above.

1. General: The quality or fact of being probable. A strong → likelihood or chance of something.
   

2. Statistics: The branch of → mathematics that studies the possible outcomes of given events and their relative distributions. → probability theory.

See also: From → probable + → -ity.

1. General: The quality or fact of being probable. A strong → likelihood or chance of something.
   

2. Statistics: The branch of → mathematics that studies the possible outcomes of given events and their relative distributions. → probability theory.

See also: From → probable + → -ity.

A curve that describes the distribution of probability over the values of a random variable.

See also: → probability; → curve.

A curve that describes the distribution of probability over the values of a random variable.

See also: → probability; → curve.