An Etymological Dictionary of Astronomy and Astrophysics

1. A particular time, especially as marked by certain circumstances or occurrences.
   

2. A special or important time, event, ceremony, celebration, etc.
   

3. A convenient or favorable time, → opportunity, or juncture (Dictionary.com).

Etymology (EN): M.E. occasioun from O.Fr. ochaison, ocasion “cause, reason, pretext; opportunity,” from L. occasionem (nominative occasio) “appropriate time,” from occasum, occasus “fall; sunset,” p.p. of occidere “fall down, go down,” from ob “down, away” + cadere “to fall,” → case.

Etymology (PE): Âkatan, from prefix â- + katan “to fall,” cf. Laki: katen “to fall,” kat “he/she fell,” beko! “fall!” (an insult);
katyâ “fallen;” Lori: kat “event, error;” Kurd. (Soriani): kawtin “to fall, befall,” kett “fallen;” Kurd. (Kurmanji): da.ketin “to fall down;” Lârestâni: kata “to fall;” Garkuyeyi: darkat, varkat “he/she fell (sudden death);” Gilaki (Langarud, Tâleš): katan “to fall,” bakatam “I fell,” dakatan “to fall (in a marsh, in a pit),” vakatan “to fall from tiredness, be exhausted,” fakatan “to fall from (i.e., lose) reputation;” Tabari: dakətə “fallen,” dakətən “to crash down,” dakət.gu “stray cow;” Proto-Iranian *kat- “to fall;” cf.
L. cadere “to fall,” → case, Pers. kâté.

1. A particular time, especially as marked by certain circumstances or occurrences.
   

2. A special or important time, event, ceremony, celebration, etc.
   

3. A convenient or favorable time, → opportunity, or juncture (Dictionary.com).

Etymology (EN): M.E. occasioun from O.Fr. ochaison, ocasion “cause, reason, pretext; opportunity,” from L. occasionem (nominative occasio) “appropriate time,” from occasum, occasus “fall; sunset,” p.p. of occidere “fall down, go down,” from ob “down, away” + cadere “to fall,” → case.

Etymology (PE): Âkatan, from prefix â- + katan “to fall,” cf. Laki: katen “to fall,” kat “he/she fell,” beko! “fall!” (an insult);
katyâ “fallen;” Lori: kat “event, error;” Kurd. (Soriani): kawtin “to fall, befall,” kett “fallen;” Kurd. (Kurmanji): da.ketin “to fall down;” Lârestâni: kata “to fall;” Garkuyeyi: darkat, varkat “he/she fell (sudden death);” Gilaki (Langarud, Tâleš): katan “to fall,” bakatam “I fell,” dakatan “to fall (in a marsh, in a pit),” vakatan “to fall from tiredness, be exhausted,” fakatan “to fall from (i.e., lose) reputation;” Tabari: dakətə “fallen,” dakətən “to crash down,” dakət.gu “stray cow;” Proto-Iranian *kat- “to fall;” cf.
L. cadere “to fall,” → case, Pers. kâté.

1. Occurring or appearing at irregular or infrequent intervals; occurring now and then.
   

2. Intended for supplementary use when needed.
   

3. Pertaining to, arising out of, or intended for the occasion (Dictionary.com).

See also: → occasion; → -al.

1. Occurring or appearing at irregular or infrequent intervals; occurring now and then.
   

2. Intended for supplementary use when needed.
   

3. Pertaining to, arising out of, or intended for the occasion (Dictionary.com).

See also: → occasion; → -al.

An → impact crater on the → dwarf planet  → Ceres. It has a diameter of about 90 km and a depth of about 4 km.

See also: Named after the Roman agriculture deity of harrowing, a method of leveling soil.

An → impact crater on the → dwarf planet  → Ceres. It has a diameter of about 90 km and a depth of about 4 km.

See also: Named after the Roman agriculture deity of harrowing, a method of leveling soil.

1. To block or stop up (a passage or opening); obstruct. To prevent the passage of.
   

   2. Chem.: To entrap a substance (vapor, gas, liquid, solid) within another (by absorption).

Etymology (EN): From L. occludere “shut up, close up,” from ob “in front of, against” + claudere “to shut, close,” → include.

Etymology (PE): Barkolândan, from bar- “on; upon; against; before; at,” → object, + kolândan “to shut,” → include.

1. To block or stop up (a passage or opening); obstruct. To prevent the passage of.
   

   2. Chem.: To entrap a substance (vapor, gas, liquid, solid) within another (by absorption).

Etymology (EN): From L. occludere “shut up, close up,” from ob “in front of, against” + claudere “to shut, close,” → include.

Etymology (PE): Barkolândan, from bar- “on; upon; against; before; at,” → object, + kolândan “to shut,” → include.

1. The process of occluding. Something that occludes.
   

   2. Phonetics: Closure at some point in the vocal tract that blocks the flow of air in the production of an oral or nasal stop (TheFreeDictionary.com).

   3. Chem.: An absorption process by which a substance adheres strongly to another.

See also: → occlude; → -tion.

1. The process of occluding. Something that occludes.
   

   2. Phonetics: Closure at some point in the vocal tract that blocks the flow of air in the production of an oral or nasal stop (TheFreeDictionary.com).

   3. Chem.: An absorption process by which a substance adheres strongly to another.

See also: → occlude; → -tion.

1. Occluding or tending to occlude.
   

   2. Phonetics: An oral or nasal stop. → occlusive consonant.

See also: → occlude; → -ive.

1. Occluding or tending to occlude.
   

   2. Phonetics: An oral or nasal stop. → occlusive consonant.

See also: → occlude; → -ive.

A → phoneme that is produced following the obstruction of air flow in the → pharynx. The sound arises during the exhalation when the air passage is no longer blocked. English occlusive consonants are [p],[b],[t],[d],[k], and [g]. Same as → stop consonant.

See also: → occlude; → -ive.

A → phoneme that is produced following the obstruction of air flow in the → pharynx. The sound arises during the exhalation when the air passage is no longer blocked. English occlusive consonants are [p],[b],[t],[d],[k], and [g]. Same as → stop consonant.

See also: → occlude; → -ive.

The blocking of light from an astronomical object, such as a star,
by another object, such as the Moon or an asteroid, that passes in front of it. Also, the period of time for which this blocking takes place. A → solar eclipse is a particular case of occultation. Determining the moment of stellar occultation by the Moon is used to improve our knowledge of the lunar orbit. Moreover, the occultation of stars by asteroids or planetary satellites provide important data for better measuring the sizes of the occulting bodies. See also → grazing occultation.

Etymology (EN): M.E. from L. occultation- “a hiding,” from occultat(us), p.p. of occultare “to conceal, keep something hidden,” frequentative of occulere “to cover over, conceal,” from ob “over” + a verb related to celare “to hide,” from PIE base *kel- “to conceal.”

Etymology (PE): Forupušân, from foru- “down, downward; below; beneath” (Mid.Pers. frôt “down, downward;” O.Pers. fravata “forward, downward;” cf. Skt. pravát- “a sloping path, the slope of a mountain”) + pušân p.pr. of pušândan, accusative of pôšidan, pôš- “to cover; to wear” (related to pust “skin, hide;” Mid.Pers. pôst; O.Pers. pavastā- “thin clay envelope used to protect unbaked clay tablets;” Skt. pavásta- “cover,” Proto-Indo-Iranian *pauastā- “cloth”).

The blocking of light from an astronomical object, such as a star,
by another object, such as the Moon or an asteroid, that passes in front of it. Also, the period of time for which this blocking takes place. A → solar eclipse is a particular case of occultation. Determining the moment of stellar occultation by the Moon is used to improve our knowledge of the lunar orbit. Moreover, the occultation of stars by asteroids or planetary satellites provide important data for better measuring the sizes of the occulting bodies. See also → grazing occultation.

Etymology (EN): M.E. from L. occultation- “a hiding,” from occultat(us), p.p. of occultare “to conceal, keep something hidden,” frequentative of occulere “to cover over, conceal,” from ob “over” + a verb related to celare “to hide,” from PIE base *kel- “to conceal.”

Etymology (PE): Forupušân, from foru- “down, downward; below; beneath” (Mid.Pers. frôt “down, downward;” O.Pers. fravata “forward, downward;” cf. Skt. pravát- “a sloping path, the slope of a mountain”) + pušân p.pr. of pušândan, accusative of pôšidan, pôš- “to cover; to wear” (related to pust “skin, hide;” Mid.Pers. pôst; O.Pers. pavastā- “thin clay envelope used to protect unbaked clay tablets;” Skt. pavásta- “cover,” Proto-Indo-Iranian *pauastā- “cloth”).

The act of occupying; the state of being occupied.

See also: Verbal noun of → occupy.

The act of occupying; the state of being occupied.

See also: Verbal noun of → occupy.

The energy level adopted by a particle, atom, or molecule under quantum mechanical laws.

See also: Occupied, p.p. of → occupy;
→ level.

The energy level adopted by a particle, atom, or molecule under quantum mechanical laws.

See also: Occupied, p.p. of → occupy;
→ level.

To take or fill up (space, time); to take possession and control of a place.

Etymology (EN): From O.Fr. occuper, from L. occupare “take over, seize, possess, occupy,” from ob “over” + intensive form of capere “to grasp, seize, take;” PIE base *kap- “to grasp” (cf. Skt. kapati “two handfuls;” Gk. kaptein “to swallow,” O.Ir. cacht “servant-girl,” literally “captive;” Goth. haban “have, hold;”
O.E. habban “to have, hold,” probably Mod.Pers. qâp-, qâpidan “to seize;”
Av. haf-, hap- “to keep, observe.”

Etymology (PE): Hagidan, from dialectal Pers.: Šahmirzâdi hâgetan, Saraxsi hagiton, Tabari hâytan, haytan,
Semnâni hâtan, Gilaki hâgitan, Lâsgardi agiton, degiton “to occupy;”
maybe related to Av. haz- “to occupy;” Skt. sah- “to overcome, be victorious, prevail,” saha- “victory,” sahate “overcomes, masters;” Gk. ekhein “to have, hold;” PIE base *segh- “to have, to hold.”

To take or fill up (space, time); to take possession and control of a place.

Etymology (EN): From O.Fr. occuper, from L. occupare “take over, seize, possess, occupy,” from ob “over” + intensive form of capere “to grasp, seize, take;” PIE base *kap- “to grasp” (cf. Skt. kapati “two handfuls;” Gk. kaptein “to swallow,” O.Ir. cacht “servant-girl,” literally “captive;” Goth. haban “have, hold;”
O.E. habban “to have, hold,” probably Mod.Pers. qâp-, qâpidan “to seize;”
Av. haf-, hap- “to keep, observe.”

Etymology (PE): Hagidan, from dialectal Pers.: Šahmirzâdi hâgetan, Saraxsi hagiton, Tabari hâytan, haytan,
Semnâni hâtan, Gilaki hâgitan, Lâsgardi agiton, degiton “to occupy;”
maybe related to Av. haz- “to occupy;” Skt. sah- “to overcome, be victorious, prevail,” saha- “victory,” sahate “overcomes, masters;” Gk. ekhein “to have, hold;” PIE base *segh- “to have, to hold.”

1. To happen; take place; come to pass.
   

2. To be found or be present; exist.

Etymology (EN): M.Fr. occurrer “to happen unexpectedly” or directly from L. occurrere “run to meet, run against, present itself,” from ob “against, toward” + currere “to run,” → current.

Etymology (PE): Roxdâdan, literally “to appear,” from rox “appearance; aspect; face,” variant ruy “face, surface” + dâdan “to give,” → event.

1. To happen; take place; come to pass.
   

2. To be found or be present; exist.

Etymology (EN): M.Fr. occurrer “to happen unexpectedly” or directly from L. occurrere “run to meet, run against, present itself,” from ob “against, toward” + currere “to run,” → current.

Etymology (PE): Roxdâdan, literally “to appear,” from rox “appearance; aspect; face,” variant ruy “face, surface” + dâdan “to give,” → event.

1. The action, fact, or instance of occurring.
   

2. Something that happens; event; incident (Dictionary.com).

3. Logic: → bound occurrence; → free occurrence.

See also: Verbal noun of → occur.

1. The action, fact, or instance of occurring.
   

2. Something that happens; event; incident (Dictionary.com).

3. Logic: → bound occurrence; → free occurrence.

See also: Verbal noun of → occur.

The intercommunicating body of salt water occupying the depressions of the Earth’s surface, or one of its major primary subdivisions, bounded by the continents, or the equator, and other imaginary lines. A sea is subdivision of an ocean.

the vast body of salt water that covers almost three fourths of the earth’s surface.

Etymology (EN): M.E. ocean(e), from O.Fr. occean, from L. oceanus, from Gk. okeanos “the great river or sea surrounding the disk of the Earth,
as opposed to the Mediterranean,” of unknown origin. Personified as Oceanus, son of Uranus and Gaia and husband of Tethys.

Etymology (PE): Oqyânus, from Ar., ultimately from Gk., as above.

The intercommunicating body of salt water occupying the depressions of the Earth’s surface, or one of its major primary subdivisions, bounded by the continents, or the equator, and other imaginary lines. A sea is subdivision of an ocean.

the vast body of salt water that covers almost three fourths of the earth’s surface.

Etymology (EN): M.E. ocean(e), from O.Fr. occean, from L. oceanus, from Gk. okeanos “the great river or sea surrounding the disk of the Earth,
as opposed to the Mediterranean,” of unknown origin. Personified as Oceanus, son of Uranus and Gaia and husband of Tethys.

Etymology (PE): Oqyânus, from Ar., ultimately from Gk., as above.

A hypothetical → exoplanet covered by a water envelope. The presence of such a planet stems from the implicit assumption of → Habitable Zone temperatures and a liquid water surface.

See also: → ocean; → planet.

A hypothetical → exoplanet covered by a water envelope. The presence of such a planet stems from the implicit assumption of → Habitable Zone temperatures and a liquid water surface.

See also: → ocean; → planet.

Of, living in, or produced by the ocean.

See also: → ocean; → -ic.

Of, living in, or produced by the ocean.

See also: → ocean; → -ic.

That part of the → Earth’s crust underling most of the Earth’s surface which is covered by the oceans. It has a remarkably uniform composition (mostly ~ 49% SiO₂) and thickness (mostly ~ 7 km). The ocean floor is the most dynamic part of the Earth’s surface. As a result, no part of the oceanic crust existing today is more than 200 million years old, which is less than 5% of the age of the Earth itself. New oceanic crust is constantly being generated from the → upper mantle by sea-floor spreading at → mid-ocean ridges, while other parts of the oceanic crust are being recycled back into the mantle at subduction zones.

See also: → oceanic; → crust.

That part of the → Earth’s crust underling most of the Earth’s surface which is covered by the oceans. It has a remarkably uniform composition (mostly ~ 49% SiO₂) and thickness (mostly ~ 7 km). The ocean floor is the most dynamic part of the Earth’s surface. As a result, no part of the oceanic crust existing today is more than 200 million years old, which is less than 5% of the age of the Earth itself. New oceanic crust is constantly being generated from the → upper mantle by sea-floor spreading at → mid-ocean ridges, while other parts of the oceanic crust are being recycled back into the mantle at subduction zones.

See also: → oceanic; → crust.

Any section of the narrow, continuous submarine mountain chain through all the world’s oceans. The oceanic ridge constitutes the most extensive mountain ridge on Earth, more than 65,000 km. Perhaps the best-known part of the ridge system is the → Mid-Atlantic Ridge.

See also: → oceanic; → ridge.

Any section of the narrow, continuous submarine mountain chain through all the world’s oceans. The oceanic ridge constitutes the most extensive mountain ridge on Earth, more than 65,000 km. Perhaps the best-known part of the ridge system is the → Mid-Atlantic Ridge.

See also: → oceanic; → ridge.

The study of the ocean, embracing and integrating all knowledge pertaining to the ocean’s physical boundaries, the chemistry and physics of sea water, and marine biology.

Etymology (EN): → ocean + → -graphy.

Etymology (PE): Oqyânus→ ocean + -šenâsi→ -logy.

The study of the ocean, embracing and integrating all knowledge pertaining to the ocean’s physical boundaries, the chemistry and physics of sea water, and marine biology.

Etymology (EN): → ocean + → -graphy.

Etymology (PE): Oqyânus→ ocean + -šenâsi→ -logy.

Any of various natural clays rich in ferric oxides (Fe₂O₃) and containing silica and alumina. Used as a red (→ hematite) or yellow (→ limonite) pigment.

Etymology (EN): M.E. oker, O.Fr. ocre, from L. ochra, from Gk. okhra,
from okhros “pale yellow.”

Etymology (PE): Oxrâ, loan from Gk.

Any of various natural clays rich in ferric oxides (Fe₂O₃) and containing silica and alumina. Used as a red (→ hematite) or yellow (→ limonite) pigment.

Etymology (EN): M.E. oker, O.Fr. ocre, from L. ochra, from Gk. okhra,
from okhros “pale yellow.”

Etymology (PE): Oxrâ, loan from Gk.

The notion that any hypothesis should be stripped of all unnecessary assumptions. If two hypotheses fit the observations equally well, the one that makes the fewest assumptions should be chosen.

Etymology (EN): The doctrine was formulated by William of Ockham (c.1288-c.1347),
an English Franciscan friar and scholastic philosopher. Razor from O.Fr. rasour “a razor,” from raser “to scrape, shave.”

Etymology (PE): Ostaré “razor,” from sotordan “to shave, erase, remove;”
Mid.Pers. ôstarak “removed, shaved,” ôstârišn “wiping, shaving;”
cf. Khotanese ustar- “to remove,” Sogdian (prefixed *pari-) prtr- “to wipe off, dry up,”
from Proto-Iranian *us-tar- “to remove, wipe off.”

The notion that any hypothesis should be stripped of all unnecessary assumptions. If two hypotheses fit the observations equally well, the one that makes the fewest assumptions should be chosen.

Etymology (EN): The doctrine was formulated by William of Ockham (c.1288-c.1347),
an English Franciscan friar and scholastic philosopher. Razor from O.Fr. rasour “a razor,” from raser “to scrape, shave.”

Etymology (PE): Ostaré “razor,” from sotordan “to shave, erase, remove;”
Mid.Pers. ôstarak “removed, shaved,” ôstârišn “wiping, shaving;”
cf. Khotanese ustar- “to remove,” Sogdian (prefixed *pari-) prtr- “to wipe off, dry up,”
from Proto-Iranian *us-tar- “to remove, wipe off.”

A prefix meaning eight.

Etymology (EN): From L. octo, Gk. okto, cognate with Pers. hašt, as below.

Skt. asta, Goth. ahtau, O.E. eahta (see eight).

Etymology (PE): Hašt “eight,” from Mid.Pers. hašt, O.Pers.*aštahva- “eighth;” Av. ašta; cf. Skt. astā; Ossetic ast; (Buddhist) Sogdian ‘št; Gk. okto, L. octo (Fr. huit; Sp. ocho);
P.Gmc. *akhto(u) (O.E. eahta, æhta, E. eight, O.N. atta, Ger. acht, Goth. ahtau); PIE base *oktô(u).
Octa-, oct, loaned Gk. forms, as above.

A prefix meaning eight.

Etymology (EN): From L. octo, Gk. okto, cognate with Pers. hašt, as below.

Skt. asta, Goth. ahtau, O.E. eahta (see eight).

Etymology (PE): Hašt “eight,” from Mid.Pers. hašt, O.Pers.*aštahva- “eighth;” Av. ašta; cf. Skt. astā; Ossetic ast; (Buddhist) Sogdian ‘št; Gk. okto, L. octo (Fr. huit; Sp. ocho);
P.Gmc. *akhto(u) (O.E. eahta, æhta, E. eight, O.N. atta, Ger. acht, Goth. ahtau); PIE base *oktô(u).
Octa-, oct, loaned Gk. forms, as above.

A group of eight units or figures.
Chemistry: An element, atom, or group having a valence of eight.

See also: From Gk. oktad- (stem oktás) “group of eight,” from okt-→ oct- + -ad a prefix denoting a group or unit comprising a certain number, sometimes of years (e.g. dyad; triad).

A group of eight units or figures.
Chemistry: An element, atom, or group having a valence of eight.

See also: From Gk. oktad- (stem oktás) “group of eight,” from okt-→ oct- + -ad a prefix denoting a group or unit comprising a certain number, sometimes of years (e.g. dyad; triad).

A polygon having eight angles and eight sides.

Etymology (EN): From L. octagonos, from Gk. oktagononos “eight-angled,” from okta-, → octa-, oct- “eight,” + gonia “angle,” related to gony “knee,”
L. genu “knee,” cuneus “a wedge;” Av. žnu- “knee;” Mod.Pers. zânu “knee,” Skt. janu- “knee,” kona- “angle, corner;” PIE base *g(e)neu-, see below.

Etymology (PE): Haštbar “eight-sided,” from hašt “eight,” → octa-, oct- + bar “side; breadth; breast” (Mid.Pers. var “breast;” Av. vouru “wide, broad, extended” (vourucašāni- “looking far”), related to varah- “breast;” cf. Skt. urú- “wide, broad,” úras- “breast;” Gk. eurus “wide, broad;” PIE base uer-, ueru-s“wide, broad”); haštguš, from hašt, → octa-, oct-, + guš “corner, angle,” Mid.Pers. gošak “corner.”

A polygon having eight angles and eight sides.

Etymology (EN): From L. octagonos, from Gk. oktagononos “eight-angled,” from okta-, → octa-, oct- “eight,” + gonia “angle,” related to gony “knee,”
L. genu “knee,” cuneus “a wedge;” Av. žnu- “knee;” Mod.Pers. zânu “knee,” Skt. janu- “knee,” kona- “angle, corner;” PIE base *g(e)neu-, see below.

Etymology (PE): Haštbar “eight-sided,” from hašt “eight,” → octa-, oct- + bar “side; breadth; breast” (Mid.Pers. var “breast;” Av. vouru “wide, broad, extended” (vourucašāni- “looking far”), related to varah- “breast;” cf. Skt. urú- “wide, broad,” úras- “breast;” Gk. eurus “wide, broad;” PIE base uer-, ueru-s“wide, broad”); haštguš, from hašt, → octa-, oct-, + guš “corner, angle,” Mid.Pers. gošak “corner.”

A geometric solid with eight sides.

See also: → octa-, oct-; → -hedron.

A geometric solid with eight sides.

See also: → octa-, oct-; → -hedron.

The Octant. A faint and obscure constellation, at 21h right ascension, 80° south declination, containing the south celestial pole. Its star Sigma Octantis is the closest naked-eye star to the pole, but it is so faint (magnitude 5.47) that it is practically useless as a polar star for navigation purposes. Abbreviation: Oct; Genitive: Octantis. It was introduced by the French astronomer Nicolas Louis de Lacaille (1713-1762).

Etymology (EN): From L.L. octans “eighth part of a circle,” from → octa-, oct- + -ans, as in quadrans; → quadrant.

Etymology (PE): Haštakân, → octant.

The Octant. A faint and obscure constellation, at 21h right ascension, 80° south declination, containing the south celestial pole. Its star Sigma Octantis is the closest naked-eye star to the pole, but it is so faint (magnitude 5.47) that it is practically useless as a polar star for navigation purposes. Abbreviation: Oct; Genitive: Octantis. It was introduced by the French astronomer Nicolas Louis de Lacaille (1713-1762).

Etymology (EN): From L.L. octans “eighth part of a circle,” from → octa-, oct- + -ans, as in quadrans; → quadrant.

Etymology (PE): Haštakân, → octant.

1. A portion of a circle cut off by an arc and two radii at 45°, one-eighth of the area of a circle.
   

2. A instrument incorporating a telescope, the predecessor of the → sextant, used to measure angular distances, mainly in nautical astronomy. It spanned an angular range of 45°.

Etymology (EN): From L.L. octans “eighth part of a circle,” from → octa-, oct- + -ans, as in quadrans; → quadrant.

Etymology (PE): Haštakân, from haštak “one-eigth,” from hašt “eight” (Mid.Pers. hašt, O.Pers.*aštahva- “eighth;” Av. ašta; cf. Skt. astā; Ossetic ast; (Buddhist) Sogdian ‘št; Gk. okto, L. octo (Fr. huit; Sp. ocho);
P.Gmc. *akhto(u) (O.E. eahta, æhta, E. eight, O.N. atta, Ger. acht, Goth. ahtau); PIE base *oktô(u)

• -ak, contraction of yak “one,” (Mid.Pers. êwak (Proto-Iranian *aiua-ka-); O.Pers. aiva- “one, alone;” Av. aēuua- “one, alone” (cf. Skt. éka- “one, alone, single;” Gk. oios “alone, lonely;” L. unus “one;” E. one) + -ân nuance suffix.

1. A portion of a circle cut off by an arc and two radii at 45°, one-eighth of the area of a circle.
   

2. A instrument incorporating a telescope, the predecessor of the → sextant, used to measure angular distances, mainly in nautical astronomy. It spanned an angular range of 45°.

Etymology (EN): From L.L. octans “eighth part of a circle,” from → octa-, oct- + -ans, as in quadrans; → quadrant.

Etymology (PE): Haštakân, from haštak “one-eigth,” from hašt “eight” (Mid.Pers. hašt, O.Pers.*aštahva- “eighth;” Av. ašta; cf. Skt. astā; Ossetic ast; (Buddhist) Sogdian ‘št; Gk. okto, L. octo (Fr. huit; Sp. ocho);
P.Gmc. *akhto(u) (O.E. eahta, æhta, E. eight, O.N. atta, Ger. acht, Goth. ahtau); PIE base *oktô(u)

• -ak, contraction of yak “one,” (Mid.Pers. êwak (Proto-Iranian *aiua-ka-); O.Pers. aiva- “one, alone;” Av. aēuua- “one, alone” (cf. Skt. éka- “one, alone, single;” Gk. oios “alone, lonely;” L. unus “one;” E. one) + -ân nuance suffix.

The interval between two musical notes, the fundamental components of which have frequencies in the ratio two to one.

Etymology (EN): M.E., from O.Fr. otaves, from L. octava feminine of octavus, from
→ octa-, oct- + -avus adj. suffix.

Etymology (PE): Octâv, loan from Fr. as above.

The interval between two musical notes, the fundamental components of which have frequencies in the ratio two to one.

Etymology (EN): M.E., from O.Fr. otaves, from L. octava feminine of octavus, from
→ octa-, oct- + -avus adj. suffix.

Etymology (PE): Octâv, loan from Fr. as above.

General: A group or series of eight.
Chemistry: A stable group of eight electrons which constitutes the outer electron shell of an atom of an inert gas (except helium whose only electron shell contains two electrons).

Etymology (EN): From → oct-, octa- + -et, as in duet.

Etymology (PE): Haštâyé, from haštâ “eightfold” + (y)é nuance suffix, as in dotâyé, → doublet.

General: A group or series of eight.
Chemistry: A stable group of eight electrons which constitutes the outer electron shell of an atom of an inert gas (except helium whose only electron shell contains two electrons).

Etymology (EN): From → oct-, octa- + -et, as in duet.

Etymology (PE): Haštâyé, from haštâ “eightfold” + (y)é nuance suffix, as in dotâyé, → doublet.

Eightfold; eight times as great.

Etymology (EN): L. octuplus, from octu- variant (before labials) of → oct- octa- + -plus “fold,” from base of plicare “to fold, twist.”

Etymology (PE): Haštâyi, from hašt “eight,” → oct- octa- + -tâyi, from tâ “fold, plait, ply; piece, part,” also a multiplicative suffix; Mid.Pers. tâg “piece, part.”

Eightfold; eight times as great.

Etymology (EN): L. octuplus, from octu- variant (before labials) of → oct- octa- + -plus “fold,” from base of plicare “to fold, twist.”

Etymology (PE): Haštâyi, from hašt “eight,” → oct- octa- + -tâyi, from tâ “fold, plait, ply; piece, part,” also a multiplicative suffix; Mid.Pers. tâg “piece, part.”

A → multipole consisting of eight point charges. Octupole moments are much smaller than → quadrupole moments and very much smaller than → dipole moment.

See also: → oct-; → pole.

A → multipole consisting of eight point charges. Octupole moments are much smaller than → quadrupole moments and very much smaller than → dipole moment.

See also: → oct-; → pole.

1. Of, pertaining to, or for the eyes.
   

2. Optics: An alternative term for → eyepiece.

Etymology (EN): From L. ocularis “of the eyes,” from oculus “eye,” from PIE base *ok^w- “to see;” cf; Av. aši- “(both) eyes;” E. → eye.

Etymology (PE): Cašmi, related to cašm “eye” (Mid.Pers. cašm, Av. cašman- “eye,” ākas- “to look,” from prefix ā- + Proto-Iranian *kas- “to look, appear,” cf. Skt. cáksus- “seeing”); didgâni, related to didgân “eyes,” plural of didé “eye,” from didan “to see” (Mid.Pers. ditan “to see, regard, catch sight of, contemplate, experience;” O.Pers. dī- “to see;” Av. dā(y)- “to see,” didāti “sees;” cf.
Skt. dhī- “to perceive, think, ponder; thought, reflection, meditation,” dādhye; Gk. dedorka “have seen”).

1. Of, pertaining to, or for the eyes.
   

2. Optics: An alternative term for → eyepiece.

Etymology (EN): From L. ocularis “of the eyes,” from oculus “eye,” from PIE base *ok^w- “to see;” cf; Av. aši- “(both) eyes;” E. → eye.

Etymology (PE): Cašmi, related to cašm “eye” (Mid.Pers. cašm, Av. cašman- “eye,” ākas- “to look,” from prefix ā- + Proto-Iranian *kas- “to look, appear,” cf. Skt. cáksus- “seeing”); didgâni, related to didgân “eyes,” plural of didé “eye,” from didan “to see” (Mid.Pers. ditan “to see, regard, catch sight of, contemplate, experience;” O.Pers. dī- “to see;” Av. dā(y)- “to see,” didāti “sees;” cf.
Skt. dhī- “to perceive, think, ponder; thought, reflection, meditation,” dādhye; Gk. dedorka “have seen”).