An Etymological Dictionary of Astronomy and Astrophysics

The condition which exists when two waves of the same frequency pass through their maximum and minimum values in a correlated or synchronized way.

Etymology (EN): → in; → phase.

Etymology (PE): Hamfâz, from ham- “together,” → com- + fâz→ phase.

Situated in the natural or original position or place.

Etymology (EN): From L. in, → in-; L. situ, → site.

Etymology (PE): Dar “in,” → in-; jâ, → place.

1. Prefix meaning “into, in, on, upon, toward, at;” variants im-; il-; ir- by assimilation of -n- with the following consonant. It occurs also sometimes as en, in loans from O.Fr.
   
2. Prefix meaning “not, opposite of, without.”

Etymology (EN): 1) From L. in; cf. Gk. en; P.Gmc. *in (cf. O.Fris, Du., Ger., Goth. in); O.E. in, inne “within.”
2) From L. in- “not,” cognate with Gk. an-; O.Pers./Av. an-, a- “not, without;” Skt. an-, a- “not;” P.Gmc. *un-; O.E. un-.

Etymology (PE): 1) Dar- “in,” from Mid.Pers. andar, → intra-.

2. nâ-, na “not,” ma- “not” (prohibitive); Mid.Pers. nê, ma “no, not;” O.Pers. naiy, nai “not;” Av. nôit, naē “not;” cf. Skt. ná “not;” L. ne-, in-, un-; Gk. ni; Lith. nè; O.C.S. ne “not;” PIE *ne-.
   bi- privative prefix, from Mid.Pers. abi-, O.Pers. *apaiy-, Av. apa-.
   a-, an-, from O.Pers./Av. negation prefix appearing before consonants and vowels respectively.
   A couple of examples in Mod.Pers.: amordâd “immortality, name of the fifth month in the Iranian calendar,” anušé; “fortunate, happy,” anirani “non Iranian,” âhu “vice, defect,” âsoqdé “unburnt, half-burnt wood.”

A group to which the speaker, the person spoken of, etc. belongs.

Etymology (EN): → in-; → group.

Etymology (PE): Xodi “insider, familiar, friend,” from xod “own,” → self-.

The quality or condition of being inaccurate.
The difference between the input quantity applied to a measuring instrument and the output quantity indicated by that instrument. The inaccuracy of an instrument is equal to the sum of its instrument error and its uncertainty.

See also: From negation prefix → in- + → accuracy

1. Not → active.
   

2. Chem.: Not → reactive.

See also: → in-; → active.

State of glowing at high → temperature; white or bright-red → heat.

See also: Quality, state noun from → incandescent.

1. (Of light) produced by → incandescence.
   

2. Glowing or → white with → heat.
   

3. Intensely → bright; brilliant (Dictionary.com).

Etymology (EN): From Fr., from L. incandescent-, incandescens, p.p. of incandescere “to become hot,” from → in- + candescere “to become hot,” from candere “to glow.”

Etymology (PE): Foruzandé, agent noun and verbal adj. from foruzidan, → glow.

Electric lamp in which light is produced by the heating effect of a → metal  → filament.

See also: → incandescent; → lamp.

1. The degree, extent, or frequency of occurrence, especially of something unwanted.
   

2. The act of striking a → light ray or → beam of particles on a surface. Also the direction of striking.

Etymology (EN): M.E., from M.Fr. incidence, from L.L. incidentia, from incidere “to happen, befall,” from in- “on” + -cidere, combining form of cadere “to fall,” → case.

Etymology (PE): Fotâd,literally “fall, the act of falling,” from fotâdan “to fall,” variant of oftâdan “to fall; to happen,” → coincide.

Same as → angle of incidence.

See also: → incidence; → angle.

1. An instance of something happening; an event or occurrence.
   

2a) Likely or apt to happen.

2b) Falling or striking on something, as light rays or a beam of particles.

Etymology (EN): → incidence.

Etymology (PE): Fotân, agent noun and adj. from fotâdan, → incidence.

The → light ray that strikes a surface before → reflection, → refraction, or → absorption. Opposite of → emergent ray.

See also: → incident; → ray.

To cut into; to cut marks upon.

Etymology (EN): M.E., from O.Fr. enciser, from L. incisus, p.p. of incidere “to cut into, cut through,” from → in- +
caedere “to cut,” → precise.

Etymology (PE): Darsunidan, from dar, → in- + sun “cut,” → precise.

The act of incising. A cutting into, especially for surgical purposes.

See also: Verbal noun of → incise.

To stir, encourage, or urge on; stimulate or prompt to action (Dictionary.com).

See also: → in-; → excite.

The act of inciting. The state of being incited. motive.

See also: Verbal noun of → incite.

1. The angle between two lines or two planes.
   
2. An orbital element that defines the angle between the orbital plane of a solar system body (planet, comet, asteroid) and the plane of the ecliptic.
   
3. The angle between the equatorial and orbital planes of a planet.

Etymology (EN): Inclination, from M.E. inclinacioun, from L. inclination-, from inclinat(us) p.p. of inclinare, from → in- + clinare “to bend;” cf. Gk. klinein “to cause to slope, slant, incline;” Skt. sri- “to lean,” O.Pers. θray-; Av. sray- “to lean;” Mod.Pers. kil “bent, inclined, slant;” PIE base *klei- “to lean, incline” from which is also derived
P.Gmc. *khlinen (Ger. lehnen, E. lean).

Etymology (PE): Darkil, from prefix dar- “in” + kil “bent, crooked, inclined” [Dehxodâ], Mid.Pers. xwahl “bent, crooked” (Mod.Pers. dialectal/colloquial variants kowleh, cowleh, cowl, caval, xohl, xohal, hol), cf. Skt. kûla- “slope, declivity;” PIE base *klei-, as above.

The angle between the rotation axis of a planet and the normal to the ecliptic.

See also: → inclination; → axis.

→ obliquity of the ecliptic.

See also: → inclination; → Earth; → equator.

To deviate from the vertical or horizontal; slant.

See also: Verbal form of → inclination.

To comprise as a part. See also → conclude, → exclude.

Etymology (EN): From L. includere “to shut in, enclose, imprison, insert,” from → in- “in” + claudere “to shut, close; to block up, make inaccessible,” ultimately from PIE root *klau- “hook, hooked branch or piece of wood; bolt, bar;” cf. L. clavis
“key,” clavus “nail,” claustrum “bar, bolt, barrier;” Gk. kleidos “bar, bolt, key;” O.Ir. clo “nail;” M.Ir. clithar “hedge, fence;” O.C.S. kljuci “hook, key,” kljuciti “shut;” Lith. kliuti “to catch, be caught on;” O.H.G. sliozan “shut,” Ger. schließen “to shut,” Schlüssel “key.”

Etymology (PE): Darkolândan, from dar-, → in-, + kolândan “to shut,” from kolân “wooden bolt, latch;” variants kelân, kolun, kolum, koland, kolandân, kelid, kelidân “wooden bolt, latch;” kalâk “a crook stick for gathering fruit;” (Tabari) kali, (Lori) kelil, (Laki) kalil “key; lock;” (Kurd.) kilil, kilij “key;” (prefixed) biškal(a) “a crooked stick for opening a lock, a sort of key;” (Kurd. Kurmanji) kelemce “handcuff;” (štiyâni) keleku “a large wooden mallet used by bleachers;” (prefixed) eškelak “a piece of wood used between a thief’s fingers to force him confess;” kor-mix, gol-mix “a large-headed peg or stake;” Mid.Pers. kilêl “key.” This family of Pers. words is probably related to PIE root *klau- “hook, hooked branch or piece of wood; bolt, bar,” as above.

1. The act of including; the state of being included; that which is included.
   

2. Fragment of foreign material enclosed within the mass of a → mineral or → meteorite. See also → CAI meteorite.

See also: Verbal noun of → include.

The lack of a fixed phase relationship between two or more waves. → coherent.

See also: Incoherent, from negation prefix → in- + → coherent; → wave.

1. The condition of two things being so different in nature as to be unable to exist together.
   

   2. Logic: (Of two or more propositions) unable to be true simultaneously.

See also: → incompatible; → -ity.

Of two or more propositions, unable to be true simultaneously. → compatible.

Etymology (EN): From M.L. incompatibilis, from → in- “not” + compatibilis (→ compatible).

Etymology (PE): Nâsâzgâr, from nâ- “not,” → in-,

• sâzgâr, → compatible.

The state of being incomplete, for example in photometric studies of a population of stars when the faintest members of the population are lacking. → completeness

See also: Negative of → completeness.

A flow whose volume or density does not change under pressure, and therefore its density is a constant. In other words, an ideal flow in which the → divergence of velocity is zero.
→ compressible flow.

See also: → incompressible, from → in “not” +
→ compressible; → flow.

1. Lack of consistency or agreement; incompatibility; an inconsistent feature or quality.
   

   2. Logic: The property of being inconsistent; a self-contradictory proposition (TheFreeDictionary.com).

See also: → in-; → consistency.

1. Lacking in consistency, agreement, or compatibility; at variance.
   

   2. Containing contradictory elements.
      

   3. Maths: (of two or more equations) not having one common set of values of the variables: x + 2y = 5 and x + 2y = 6 are inconsistent
      

   4. Logic: (of a set of propositions) Enabling an explicit contradiction to be validly derived (TheFreeDictionary.com).

See also: → in-; → consistent.

1. To make or become greater, in number, size, degree, etc..
   

2. The act of increasing. The amount by which something increases.

Etymology (EN): M.E., from O.Fr. encreiss-, pr.p. stem of encreistre, from L. increscere “to increase, to grow upon,” from → in- “in” + crescere “to grow,” → crescent.

Etymology (PE): Afzudan, from Mid.Pers. abzudan “to increase, grow,” O.Pers. abijav- “to increase, add to, promote,” from abi-, aiby- “in addition to; to; against” + root jav- “press forward,” Av. gav- “to hasten, drive,” Sk. jav- “to press forward, impel quickly, excite,” javate “hastens.”

The amount by which a varying quantity increases between two of its stages. In → calculus, the Greek letter Δ (delta) is used to denote an increment; e.g. Δx is an increment of x, contrasted to → decrement.

Etymology (EN): Increment, from L. incrementum “growth, increase,” from stem of increscere “to grow in or upon” from → in- “in” + crescere “to grow.”

Etymology (PE): Fazâyé, from fazâ shortened present stem of afzudan “to add, increase” (Mid.Pers. abzudan “to increase, grow;” O.Pers. abijav- “to increase, add to, promote,” from abi-, aiby- “in addition to; to; against” + root jav- “press forward;” Av. gav- “to hasten, drive;” Skt. jav- “to press forward, impel quickly, excite,” javate “hastens”) + -y- euphonic infix + -é noun/nuance suffix.

Not → definite; without fixed or specified limit.

See also: From → in- “not, without” + → definite.

Math.: An integral without upper and lower limits. The general antiderivative of
a function. → definite integral.

See also: → definite; → integral.

Not dependent.

See also: From negation prefix → in- + → dependent.

Statistics: Two events if the occurrence of one of them gives
no → information about whether or not the other event will occur; these events have no influence on each other.

See also: → independent; → event.

Statistics: Two random variables X and Y
if and only if the value of X has no influence on the value of Y and vice versa.

See also: → dependent; → random; → variable.

Math.: A variable whose value determines the value of other variables.
For example, x, in the expression y = f(x), is the independent variable.
See also → dependent variable.

See also: → independent; → variable.

Philosophy: The doctrine that there are events which do not correspond with determinism and therefore are uncaused in some sense.
Quantum physics: The claim that the most basic constituents of matter behave indeterministically, in accordance with such properties as the → uncertainty principle.

Etymology (EN): → in-; → determinism.

Etymology (PE): Nâtarmbâvari, nâtarmvari, from nâ- negation prefix

• (â)tarmbâvari, (â)tarmvari, → determinism.

1. Math.: A number or symbol, often written as a → subscript or → superscript to a mathematical expression, that indicates an operation to be performed, an ordering relation, or a use of the associated expression.
   

2. Physics: A measure of a particular property; e.g. → adiabatic index; → color index; → index of refraction.
   

3. In some → astrolabes, the → rule.
   

4. A sequential arrangement of items, especially in alphabetical or numerical order. → Index Catalogue.

Etymology (EN): Index, from L. index “forefinger, pointer, sign,” literally
“anything which points out,” from indicare “point out, show,” from in- “in” + dicare “to proclaim,” from stem of dicere
“to speak, to say;” PIE base *deik- “to point out” (cf. Av. daēs- " to show;" Skt. dic- “to point out, show;” Gk. deiknynai “to prove;” O.H.G. zeigon; Ger. zeigen “to show;” O.E. teon “to accuse,” tæcan “to teach”).

Etymology (PE): 1) Dišan, from diš-, simple aorist of Av. daēs- “to show,” as above, + suffix -an.
2) Fehrest, from Mid.Pers. payrâstag “arranged,” from payrâstan “to arrange; to adorn” (Mod.Pers. pirâstan); Proto-Ir. *pati-rāsta-, from *pati “to, at, for, in” (cf. Mid.Pers.
pad “to, at, for, in;” Mod.Pers. be, beh;
Old.Pers. paity; Av. paiti “to, toward, in, at;”
Skt. práti; Gk. poti) + *rād- “to direct, arrange”
(cf. Mod.Pers. raj “line, row,” variants raž, rak, râk, rezg (Lori), ris, risé, radé, rasté, râsté, related to râst “right, true; just, upright, straight;” Mid.Pers. râst “true, straight, direct;” Sogdian rəšt “right;” O.Pers. rāsta- “straight, true,” rās- “to be right, straight, true;” Av. rāz- “to direct, put in line, set,” razan- “order;”
cf. Skt. raj- “to direct, stretch,” rjuyant- “walking straight;” Gk. orektos “stretched out;” L. regere “to lead straight, guide, rule,” p.p. rectus “right, straight;” PIE base *reg- “move in a straight line,” hence, “to direct, rule”).

Either of two catalogues of non-stellar objects, which serve as supplements to the → New General Catalogue.

See also: → index; → catalog

Same as → refractive index.

See also: → index; → refraction.

The → numeral system consisting of the numerals 0, 1, 2, 3, 4, 5, 6, 7, 8, and 9 which evolved into the system we use today. The Indian numerals was a place-value or positional system. The Indians were the first to develop a base 10 positional system. Same as → Hindu-Arabic numeral system.

See also: Indian, from India, → Indus; → numeral; → system.

A color between blue and violet.

Etymology (EN): From Sp. indico, Portuguese endego, and Du. (via Portuguese) indigo, from L. indicum “indigo,” from Gk. indikon “blue dye from India,” literally “Indian (substance),” neuter of indikos “Indian,” → Indus.

Etymology (PE): Nil “indigo color; the indigo plant;” Mid.Pers. nil; cf. Skt. nīlī, nīlā “the indigo plant; indigo color.”

Not in a direct course, path, action, or procedure.

See also: → in-; → direct.

A word or group of words representing the person or thing with reference to which the action of a verb is performed. In English generally coming between the verb and the direct object and paraphrasable as the object of a preposition, usually to or for, following the direct object, as the boy in He gave the boy a book (Dictionary.com).

See also: → indirect; → object.

1a) A single human being, as distinguished from a group (Dictionary.com).

1b) A distinct, indivisible entity; a single thing, being, instance, or item
(Dictionary.com).

1c) Logic: An → object or element taken as the → subject of the → predicates of → first-order logic.

2. Of, pertaining to, or characteristic of a particular person or thing. → individual constant, → individual variable.

Etymology (EN): M.E., from M.L. individualis, from L. individuus “indivisible,” from → in- “not, opposite of” + dividuus “divisible,” from dividere, → divide.

Etymology (PE): Takâl, from tak, → single, + suffix -âl, → -al; takâli with adj. suffix -i.

In predicate logic: A → word or → expression that represents a → specific  → individual or → object. A single object can be denoted by multiple individual constants, reflecting the fact that objects can have multiple names. On the other hand, any individual constant can only denote one object. Individual constants are represented by lower case letters from the beginning of the alphabet: a, b, c.

See also: → individual; → constant.

In → predicate logic,
a variable which represents an unspecified → subject. Individual variables work just as do variables in algebra, they stand in for a value, but have no fixed value of their own. They are represented by lower case letters taken from the end of the alphabet x, y, z; and if additional variables are needed by u, v, w, as well.

See also: → individual; → variable.

1. A social theory advocating the liberty, rights, or independent action of the individual (Dictionary.com).
   

2. An individual peculiarity.

See also: → individual; → -ism.

1. A person who shows great independence or individuality in thought or action (Dictionary.com).
   

2. An advocate of → individualism (Dictionary.com).

See also: → individual; → -ist.

The particular character, or aggregate of qualities, that distinguishes one person or thing from others (Dictionary.com).

See also: → individual; → -ity.

The process or state of discriminating the individual from the generic group or species.

See also: → individualize; → -tion.

To make individual or distinctive; give an individual or distinctive character to (Dictionary.com).

See also: → individual; → -ize.

To cause or initiate by influence or some means; e.g. → induced current; → induced emission.

Etymology (EN): Induce, “to lead by persuasions or other influences,” from L. inducere “to lead into, persuade,” from → in- “in”

• ducere “to lead,” from PIE *deuk- “to lead” (cf. O.E. togian “to pull, drag,” O.H.G. ziohan “to pull”).

Etymology (PE): Darhâxtan, darhâzidan, from dar- “in” + Mid.Pers. hâxtan, hâzidan, “to lead, guide, persuade;”
Av. hak-, hacaiti “to attach oneself to, to join;” cf. Skt. sacate “accompanies, follows;” Gk. hepesthai “to follow,"; L. sequi “to follow;” PIE *sek^w- “to follow.”

Brought about or caused by → induction.

See also: Induced, p.p. of → induce.

Current resulting from the relative motion of a conductor through a magnetic field.

See also: → induced ; → current.

An electric field created by the variation of a magnetic field. The induced electric field lines are usually perpendicular to the changing magnetic field that produces them.

See also: → induced; → electric; → field.

The emission of radiation from an atom when it is bombarded by photons. The induced radiation has the same wavelength and direction as the bombarding radiation. Same as → stimulated emission.

See also: → induced; → emission.

Fission which takes place when a nucleon is bombarded with neutrons or high-energy radiation (gamma rays).

See also: Induced, p.p. of → induce; → fission.

The property of an electric circuit, or of two neighboring circuits, by virtue of which an electromotive force is induced in one circuit by a change of current in either of them.

See also: Inductance, from induct, from L. inductus, p.p. of
→ induce + → -ance.

1. General: The act of inducing, bringing about, or causing.
   

2. Electromagnetism: A common term for the process by which a body having electric or magnetic properties produces magnetism, an electric charge, or an → electromotive force in a neighboring body without contact. For more details, see → electromagnetic induction; → electrostatic induction; → magnetic induction.
   

3. Math.: A method of mathematical proof typically used to establish that a given statement is true of all natural numbers. It is done by proving that the first statement in the infinite sequence of statements is true, and then proving that if any one statement in the infinite sequence of statements is true, then so is the next one.
   

4. Logic: Any form of reasoning in which the conclusion, though supported by the premises, does not follow from them necessarily. → inductive reasoning.

See also: Verbal noun of → induce.

A device for producing high-voltage pulses by means of → electromagnetic induction. It consists of a primary coil of a few turns of wire, wound on an iron core, and insulated from a secondary coil of many turns which surrounds it coaxially. The current in the primary, which is interrupted periodically, sets up a magnetic field, first big, then zero. This changing field induces a large voltage in the secondary.

See also: → induction; → coil.

In magnetohydrodynamics, an equation that describes the transport of plasma and magnetic field lines over time:
∂B/∂t = ∇ x (v x B) + η∇²B,

where B is the → magnetic induction, v is the plasma velocity, and η = (μσ)^-1 the → magnetic diffusivity. The first term on the right side represents → magnetic advection and the second term → magnetic diffusion.
The induction equation can also be expressed as:
∂B/∂t = -(v.∇)B + (B.∇)v - B(∇.v),

where the terms of the right-hand side stand for advection, stretching, and compression, respectively. Among these terms, net increase of the field can be done only through the stretching and compression.

See also: → induction; → equation.

A component of an electromagnetic field which is
the region close to the source (an antenna) where steady-state magnetic and electrostatic forces can be detected. → radiation field.

See also: → induction; → field.

Of, relating to, or using → induction. induction

See also: From induct, → induce, + → -ive.

Reasoning from detailed facts to general principles.

See also: → deductive; → reasoning.

A coil of wire used to introduce inductance into an electric circuit.

See also: Agent noun of → induce.

The American Indian. A faint, southern constellation (right ascension: 21 hours, declination: -55 degrees), supposed to represent an American native Indian. It was introduced in the 1603 star atlas of Johann Bayer and contains no stars brighter than the third magnitude. Abbreviation: Ind; genitive: Indi.

Etymology (EN): Indus “an Indian,” from L., from Gk. Indos “the Indus River, an Indian.”

Etymology (PE): Sorxpust “red skin,” the term coming from the reddish skin color of some native Americans, from sorx, → red, + pust “skin,” from Mid.Pers. pôst “skin;” Av. pastô-, in pastô.fraθanhəm “of the breadth of the skin.”
Hendi “Indian,” Mid.Pers. Hindûk, from Hind “Indian;” O.Pers. hindu- “Sind, a province of the Persian Empire on the upper Indus River,” Hinduya- “man of Sind;” Av. hindu-, həndu-; Skt. sindhu- “stream; the Indus; country around the Indus.”

A collision between bodies in which there is a loss of total kinetic energy.

See also: → inelastic; → collision.

A type of scattering when the → scattered radiation has a → wavelength different from that of the → incident radiation (→ Raman scattering, → fluorescence ).

See also: → inelastic; → scattering.

1. A statement of the form a ≠ b, a > b, or a < b, asserting one quantity is greater than or less than another quantity. → equality.
   
2. An irregularity in the movement of a celestial object in its orbit about another which cannot be explained by their mutual gravitational attraction. Irregularities are often due to perturbation by other neighboring objects.

See also: → in-; → equality.

Having no inherent power of action, motion, or resistance (opposed to active).
Chemistry: A chemically inactive element, compound or material. → inert gas.

Etymology (EN): Inert, from Fr. inerte, from L. inertem “unskilled, inactive,” from → in- “without” + ars (gen. artis) “skill.”

Etymology (PE): Laxt “sluggish, inert.”

Any one of six gases helium, neon, argon, krypton, xenon, and radon, all of whose atomic shells contain complete numbers of electrons so that the atoms are almost completely chemically inactive. Same as noble gases.

See also: → inert; → gas.

Tendency of a body to preserve its state of rest or uniform motion in a straight line.

Etymology (EN): Inertia, from L. inertia “un-skillfulness, idleness,” from iners (gen. inertis) “unskilled, inactive;” → inert.

Etymology (PE): Laxti “sluggishness, inertia.”

An ellipsoid used in describing the motion of a rotating rigid body. It is stationary with respect to the rotating body, and is determined by the body’s moments of inertia.

See also: → ellipsoid; → inertia.

Of or relating to inertia.

Etymology (EN): From → inertia + → -al.

Etymology (PE): Laxt, adj. of laxti, → inertia

A force arising from the → acceleration of an observer’s → frame of reference.

See also: → inertial; → force.

→ inertial reference frame.

See also: → inertial; → frame.

The mass of a body as determined from the acceleration of the body when it is subjected to a force that is not due to gravity.

See also: → inertial; → mass.

Motion free of any force, with constant velocity.

See also: → inertial; → motion.

1. A periodic motion of a particle that moves, free from external forces, over the surface of a rotating sphere, such the Earth. Inertial oscillations result from the → Coriolis force. For example, a hockey puck launched on a big enough lake in the northern hemisphere would turn to the right (east) and eventually loop back to nearly the initial point (actually west of that point). The time it takes for the huckey puck to return can be computed with the → Coriolis frequency.
   

2. Meteo.: An anticyclonic (clockwise) rotation in the northern hemisphere, with the Coriolis force providing the → centripetal acceleration with period of 2π/f, where f is the Coriolis frequency. The opposite should occur in the southern hemisphere.

See also: → inertial; → oscillation.

A → reference frame or coordinate system in which there are no accelerations, only zero or uniform motion in a straight line. According to the special theory of relativity, it is impossible to distinguish between such frames by means of any internal measurement.

See also: → inertial; → reference; → frame.

The fall of matter toward the center of a region of gravitational influence.

Etymology (EN): Infall, from → in- + → fall.

Etymology (PE): Darun-oft, from darun- “in, into; within” (Mid.Pers. andarôn
“inside,” from andar, → inter-, + rôn “side, direction;” Av. ravan- “(course of a) river”)

• oft, → fall.

To affect, cause infection, or contaminate with a pathogenic microorganism or agent.

Etymology (EN): M.E. infecten, from L. infectus, p.p. of inficere “to immerse in dye, discolor, taint, poison,” from equivalent to → in- + → -fac, combining form of facere “to do, make,” → fact, + -tus p.p. suffix; from PIE root *dhe- “to set, put.”

Etymology (PE): Fažidan, infinitive from faž “dirt, filth, pus;” related word faže, fažnâk, fažgen, fažegen, fažgin, fažqand “filthy, dirty;” of unknown origin. It may be related to Proto-Ir. root *xard- “to defecate,” with offshoots xard “muddy place,” xarra “mud,” (+ *pati-) payxâl “excrement.”

1. A thing that infects or causes infection.
   

   2. Causing infection; infecting.

See also: → infect; → -ant.

1. Affected with a disease-causing organism.
   

   2. Computers: Affected with a → virus.

See also: P. p. of → infect.

A branch of medicine that deals with the diagnosis, management and treatment of various infectious or contagious diseases.

See also: → infection; → -logy.

1. An act or fact of infecting; state of being infected.
   

   2. An infecting agency or influence.
      

   3. An infectious disease.
      

   4. Computers: The presence of a virus in, or its introduction into, a computer system.

See also: Verbal noun of → infect.

1. Capable of causing infection.
   

2. Caused by or capable of being transmitted by infection.

See also: → infect(ion) + -ious, variant of → -ous.

Capable of causing infection.

See also: → infect; → -ive.

1. The act or process of deriving logical conclusions from premises known or assumed to be true.
   
2. Something that is inferred.

Etymology (EN): From M.L. inferentia, from inferre, from → in- “in” + ferre “to carry, bear,” cognate with Pers. bordan “to carry, bear,” as below.

Etymology (PE): Darbord (on the models of daryâft “perception” and peybord “understanding, finding;” see also bâzbord, → reference), from dar-, → in-,

• bord past stem of bordan “to carry, bear;” (Mid.Pers. burdan; O.Pers./Av. bar- “to bear, carry,” Av. barəθre “to bear (infinitive);” Skt. bharati “he carries;” Gk. pherein; L. fero “to carry;” PIE base *bher- “to carry”).

Lower in place or position; closer to the bottom or base.
Astro.: → inferior conjunction;
→ inferior culmination; → inferior planet.

Etymology (EN): From L. inferior “lower,” comp. form of inferus (adj.) “that is below or beneath,” from infra “below” (→ infrared), cognate with Pers. zir, as below.

Etymology (PE): Zirin, adj. from zir “below, down,” Mid.Pers. azêr “below, under,” êr “below, down; low, under,” adar “low;”
Av. aδara- (adj.), aδairi- (prep.) “below;” cf. Skt. ádhara- “lower;” L. infra (adv., prep.) “below, underneath, beneath,” inferus “lower;” O.E. under “under, among”);
PIE base *ndher.

The conjunction of an inferior planet with the Sun when the planet is between the Sun and the Earth. → superior conjunction.

See also: → inferior; → conjunction.

The meridian transit of a star between the celestial pole and the north point of the horizon. Same as → lower culmination. → superior culmination.

See also: → inferior; → culmination.

A planet that orbits between the Earth and the Sun. Mercury and Venus are the only two inferior planets in the Solar System.

See also: → inferior; → planète.

Unlimited or unmeasurable in extent of space, duration of time, etc.
Math.: Not finite; an infinite quantity or magnitude; large beyond bound.
Of a set, having elements that can be put into one-to-one correspondence with a subset that is not the given set.

See also: → in- + → finite.

A → statistical population consisting of individuals or items which either possesses the infinite property through some limiting process or is non-enumerable. For example, the population of all → real numbers between 0 and 1 and the population of all → integers are examples of infinite population. In case of random sampling with replacement, any population is always infinite.

See also: → infinite; → population.

A series with infinitely many terms, in other words a series that has no last term, such as 1 + 1/4 + 1/9 + 1/16 + · · · + 1/n² + … .

The idea of infinite series is familiar from decimal expansions, for instance the expansion π = 3.14159265358979… can be written as π = 3 + 1/10 + 4/10² + 1/10³ + 5/10⁴ + 9/10⁵ + 2/10⁶ + 6/10⁷ + 5/10⁸ + 3/10⁹ + 5/10¹⁰ + 8/10¹¹ + … , so π is an “infinite sum” of fractions. See also → finite series.

See also: → infinite; → series.

A set which can be put in a one-to-one correspondence with part of itself.

Etymology (PE): → infinite; → set.

General: Indefinitely or exceedingly small.
Math.: A variable that approaches zero as a limit. A quantity decreasing indefinitely without actually becoming zero.

Etymology (EN): Infinitesimal, coined by Ger. philosopher and mathematician Baron Gottfried Wilhelm von Leibniz (1646-1716) from N.L. infinitesim(us) “infinite in rank,” from infinit(us), → infinite, + -esimus suffix of ordinal numerals + → -al.

Etymology (PE): Bikarânxord, from bikarân “unbounded, unlimited, infinite,”
from bi- “without” + karân “boundary, side, end” (variants karâné, kenâr, from Mid.Pers. karân, karânak, kenâr “edge, limit, boundary,” Av. karana- “side, boundary, end”)

• xord “minute, little, small” (from Mid.Pers. xvart, xôrt “small, insignificant;” Av. ādra- “weak, dependent;” Skt. ādhrá- “small, weak, poor,” nādh “to be oppressed;” Gk. nothros “sluggish;” PIE base *nhdhro-).

The body of rules and processes by means of which continuously varying magnitudes are dealt with in → calculus. The combined methods of mathematical analysis of → differential calculus and → integral calculus.

See also: → infinitesimal, → calculus.

The nominal form of the verb which expresses the idea of action or state without indicating person, number, or tense.

Etymology (EN): Contraction of L. infinitivus modus “unlimited, indefinite mood,” from L. infinitus, → infinite.

Etymology (PE): Karpâyé, literally “action base,” from kar-, → verb, + pâyé, → base.

That quantity which is greater than any assignable quantity.

See also: Noun form of → infinite.

1. Feeble or weak in body or health, especially because of age.
   

2. To unvalidate.

Etymology (EN): M.E. infirm, from L. infirmus “weak, frail, not strong or firm” from → in- “not, opposite of” + firmus, → firm.

Etymology (PE): Nâdeš, from nâ- “not,” → in-, + deš, → firm.

An → affix that is inserted within a root or stem.

Etymology (EN): From L. infixus p.p. of infigere “to fasten in,” from in-

• figere “fasten.”

Etymology (PE): Darvand, from dar- “in” + vand, → affix.

To become inflated; to increase, especially suddenly and substantially. → inflation, → inflatory model.

Etymology (EN): Inflate, from L. inflatus p.p. of inflare “to blow into, puff up,” from → in- “into” + flare “to blow.”

Etymology (PE): Pandâmidan “to swell,” from pandâm [Mo’in] “swelling;” Borujerdi panâm, panam “swellig;” Malâyeri panomidan “to swell;” Laki penamiyen “to swell;” Hamadâni pandumidan “swelling of the eye or other parts of the body;” Kermâni padum kerdan “to swell,” padum “swelled; fat, corpulent;” Tâleši pandâm, pandom “swelling;” Gilaki pandâm kudan “rising of river water caused by flood;” cf. Gk. pneuma “wind; breath,” from pnein “to blow; to breathe;” PIE base *pneu- “to breathe.” Related terms in other Indo-European languages: O.E. fnaeran “to breathe heavily,” fneosan “to snort, sneeze;”
M.H.G. pfnusen, pfnehen “to breathe, pant, sniff, snort, sneeze;” Norw. fnysa “to breeze;” M.Du. fniesen, Du. fniezen “to sneeze;”
O.H.G. niosan, Ger. niesen “to sneeze.”

1. General: The act of inflating; the state of being inflated.
   

2. Cosmology: A brief exponential expansion of the Universe postulated to have occurred 10^-35 seconds after the → Big Bang, in response to the separation of the → strong interaction from the → electroweak interaction. This idea aims at explaining the → flatness problem, the → horizon problem, and the → magnetic monopole problem. See also → inflaton field.

See also: Verbal noun of → inflate.

A class of → Big Bang models of the Universe that include a finite period of accelerated expansion in their early histories. Such an event would have released enormous energy, stored until then in the vacuum of space-time. The horizon of the Universe expanded, temporarily, much faster than the speed of light.
→ inflaton field.

See also: Inflationary, adj. of → inflation; → model.

The hypothetical → particle that mediates the hypothetical → inflaton field.

See also: From inflat-, from → inflaton field, + particle suffix → -on.

A hypothetical → scalar field that provides a theoretical basis for → inflation in the early → Big Bang history of the → Universe. The inflaton field would fill space with the same energy at every point. In general, the scalar field can vary with time and space, though to a first approximation everywhere in the Universe will have the same value at any time. The field has a particle associated with it, called → inflaton, just as the → electromagnetic field is associated with the → photon. The inflaton field is characterized also by a → negative pressure that would yield a tremendous → repulsive gravity during a brief lapse of time. In the earliest moments of the Universe, space is uniformly filled with an inflaton field, whose value places it higher up on its → potential energy curve. The inflaton’s → potential energy would drop
in a tiny fraction of a second, on the order of 10^-35 seconds. And yet, during that brief instant, space would expand by a colossal factor, of at least 10³⁰.

See also: → inflaton; → field.

1. General: To bend in, to turn from a direct line or course.
   
2. Grammar: To change the ending or form of a word in accordance with other words in a sentence. To apply → inflection to.

Etymology (EN): From M.E. inflecten, from L. inflectere “to bend in, bow, curve,” figuratively, “to change,” from → in- + flectere “to bend, to curve,” of uncertain origin.

Etymology (PE): Darcaftidan, from dar-, → in-, + caftidan, → flex.

A change in the form of a word to indicate a change in such grammatical features as tense, person, gender, case, number, voice, or mood. A general term for → declension and → conjugation.

See also: Verbal noun of → inflect.

A point on a → curve at which the → tangent changes direction, from rotating in one sense to rotating in the opposite sense.

See also: → inflection; → point.

Of, relating to, or characterized by the use of → inflection, e.g.
→ inflectional affix.

See also: → inflection + → -al.

An → inflection that is added at the end of a root word. In English there are eight inflectional affixes, which are all suffixes. They always follow derivational suffixes and do not change the category of a word.

See also: → inflectional + → affix.

1. The act or process of flowing in or into. Something that flows in or into. Opposite of → outflow.
   

2. Meteo: Flow of water into a stream, lake, reservoir, container, basin, aquifer system, etc.

See also: Inflow, from → in- + → flow.

1. The act or power of producing an → effect, especially inconspicuously; the effect of power exerted.
   

2. To have or exert influence on; affect.

Etymology (EN): M.E., from O.Fr. influence, from L. influentia “stellar emanation” (it was thought an ethereal liquid flowed from the stars and affected the destiny of humans), also “a flow of water,
a flowing in,” from L. influentem (nominative influens), pr.p. of influere “to flow into,” from → in- “into, in, on, upon” + fluere “to flow;” PIE base *bhleu- “to swell, overflow;” cf. Gk. phluein “to boil over, bubble up,” phlein “to abound.”

Etymology (PE): Hanâyeš “influence” (Borhân-e Qâte’; Kasravi). We suggest the following origin
for this word: ultimately from Proto-Ir. *ha-nai “to conduct, direct, guide, lead,”
from *ham-naiH-, from prefix *ham- “together,” also an intensive prefix, → com-, + *naiH- “to lead, conduct, guide;” cf. Av. naii- (naŷ-) “to lead, guide,” naiieiti “leads;”
O.Pers. nay- “to lead, bring” anaya “leads;” Mid.Pers. nidan, ônidan, nay- “to lead, bring;” Sogd. n’y- “to lead;” Choresmian (prefixed, + *apa-) bny- “to remove;” Skt. nī- “to lead,” náyati “leads.”
In dialects: Anâraki niye “to bring, lead;” Kurd. (prefixed) ânin, inân, (with prefix ham-) hânin, hênân “to bring, lead to,” Tâleši ânân, ânoe “to bring together two edges;” Zazaki ân- “to bring;” Qohrudi hunda, hun- “to bring, lead;”
Târi niya-, neg- “to lead;” Lasgardi (prefixed) bin- “to bring, carry;” Qomi niyé, Tafreši neyé “a jab or poke used for leading the cattle;” see also → relate.

1. To impart → knowledge of a fact or circumstance.
   

2. To supply (oneself) with knowledge of a matter or subject (dictionary.com).
   

3. To convey → information.
   

See also: → informatics, → information theory.

Etymology (EN): Inform, from M.E. informen, from O.Fr. enformer, from L. informare “to shape, form; to form an idea of,” from → in- “into” + → forma “form.”

Etymology (PE): Azdâyidan, from Mid.Pers. azdênidan “to inform,” from azd “information, proclamation; known” (loaned into Arm. azd), from O.Pers. azdā “known,” azdā kar “to become known;” Av. azdā “known;” Sogdian ‘zd’ “informed, known;” cf. Skt. addhā’ “manifestly; certainly, truly,” addhāti “sage.”

A person who gives → information.

See also: From → inform + -ant a suffix forming adjectives and nouns from verbs.

The science concerned with gathering, manipulating, storing, retrieving, and classifying recorded → information. Also called → information science, computer science.

See also: Informatics, from informat(ion), → information + → ics.

1. Knowledge gained through study, communication, research, instruction, etc.
   

2. Knowledge communicated or received concerning a particular fact or circumstance; news.
   

3. The act or fact of informing.
   

4. A sequence of signals that conveys a message to a receiver. Information does not exist on its own. It is contained within something and is coded. The notion of information involves → uncertainty and → randomness; hence the necessity for calling on → probability theory and → statistics.
   

See also:

→ information content, → information entropy, → information flow, → information paradox, → information science, → information technology, → information theory, → infosphere, → quantum information, → entropy.

See also: Verbal noun of → inform.

The → negative of the → logarithm of the → probability that a particular
→ message or → symbol will be emitted by a → source.

See also: → information; → content.

The measure of information, which is usually expressed by the average number of bits needed for storage or communication. In other words, the degree to which the values of a → random variable X
are dispersed. If the → probability density function of X is P(x), the entropy is defined by: H(X) = -Σ P(x) log P(x). Also called → Shannon entropy.

See also: → information; → entropy.

The flow of data into a system or to the end users.

See also: → information; → flow.

A paradox raised in 1976 by S. Hawking (1942-2018) whose analysis of the thermodynamic properties of → black holes led him to the prediction that black holes are not in fact black, but radiate due to quantum effects. This implied that, due to the → Hawking radiation, a black hole would eventually evaporate away, leaving nothing. This deduction presented a problem for → quantum mechanics, which maintains that information can never be lost.

This topic is a matter of intense debate. Many solutions have been proposed, but all of them have serious drawbacks. In order to analyze better these solutions one needs a quantum gravity theory, which does not exist at the moment.

In brief, either the idea of → quantum unitarity must be given up, or a mechanism should be found by which information is not lost after it falls into a black hole.

See also: → information; → paradox.

Same as → informatics.

See also: → information; → science.

The science and activity of receiving, storing, processing, and transmitting information by using → computers.

See also: → information; → technology.

The mathematical theory that defines, quantifies, and analyzes the concept of → information. It involves → probability theory in → transmission of → messages when the → bits of information are subject to various distortions. Its goal is to enable as much information as possible to be reliably stored on a medium, retrieved, or communicated.

See also:
→ information content, → information entropy, → information flow, → information paradox, → information science, → information theory, → quantum information, → entropy.

See also: → information; → theory.

Giving → information, providing information, imparting → knowledge.

See also: From informat-, from L. informatus, from → inform + → -ive.

A person who provides → information.

See also: From → inform + -er, → -or.

The global network of all the world’s communications, databases, and sources of information.

See also: → information; → sphere.

A prefix meaning “below,” used with second elements of any origin.
→ infrared; → infrasound.

Etymology (EN): From L. infra “below, underneath, beneath,” from PIE *ndher; cf. Mod.Pers. zir “below, down,” akin to → under-.

Etymology (PE): Foru-, from foru “down, downward; below; under, beneath; low,” from Mid.Pers. frôt “down, downward;” O.Pers. fravata “forward, downward;” cf. Skt. pravát- “a sloping path, the slope of a mountain.”

The invisible part of electromagnetic spectrum possessing wavelengths between those of visible light and those of radio waves, i.e. approximately between about 0.75 and 1000 μm.

Etymology (EN): From L. infra (adv., prep.) “below, underneath, beneath,” inferus “lower,” from PIE *ndher; cf. Av. aδara- (adj.), aδairi- (prep.) “below;” Mid.Pers. êr “below, down; low, under,” adar “low,” azêr “below, under” (Mod.Pers. zir “below, down”); Skt. ádhara- “lower;” O.E. under “under, among”); → red.

Etymology (PE): Forusorx, 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,” + sorx→ red.

A two-dimensional infrared imaging device, consisting of an array of small, individual electronic detectors, each of which records a pixel in the image.

See also: → infrared; → array.

An orbiting infrared telescope (60 cm mirror) which successfully operated from launch
in January 1983 until the supply of coolant ran out in November 1983. It was a collaborative mission between NASA, the Netherlands, and the UK, and mapped 95% of the whole sky in the wavelength bands 12, 25, 60, and 100 microns.

See also: → infrared; → astronomical; → satellite.

The study of infrared properties of astronomical objects.

See also: → infrared; → astronomy.

An optical camera equipped with a → detector which is sensitive to → infrared radiation.

See also: → infrared; → camera.

Wispy, extended structures seen above and below the plane of the Galaxy in the infrared maps of the sky (60-100 microns) produced by the → Infrared Astronomical Satellite (IRAS).

See also: → infrared; L. cirrus “curl, tuft, plant filament like a tuft of hair.”

A → dark cloud characterized by a → visual extinction A_v≥ 10² mag. IRDCs are opaque even at 8 μm, and can be seen in silhouette against the bright diffuse → mid-infrared emission in the → interstellar medium.

See also: → infrared; → dark; → cloud.

A thermal device for observing and measuring → infrared radiation.

See also: → infrared; → detector.

The portion of → electromagnetic radiation from → astrophysical objects in → infrared frequencies.

See also: → infrared; → emission.

Infrared → emission from a star in excess of that expected from a → blackbody with the temperature corresponding to the temperature of the star.

See also: → infrared; → excess.

A galaxy that emits most of its energy in the infrared region of the spectrum. Such galaxies are thought to have unusually high rates of star formation and are also described as → starburst galaxies.

See also: → infrared; → galaxy.

Imaging with an infrared detector.

See also: → infrared; → imaging.

That part of the → electromagnetic radiation lying beyond the red, between the radio and the visible regions of the → electromagnetic spectrum. The wavelengths range from about 0.8 → microns (μm) to about 1000 μm.

See also:

→ near-infrared; → mid-infrared; → far-infrared; → submillimeter radiation.

See also: → infrared; → radiation.

A European Space Agency satellite which carried the most sensitive infrared telescope ever launched. It operated between November 1995 and April 1998 and made particularly important observations of the dusty regions of the Universe.
ISO was equipped with four science instruments: an infrared camera (CAM), a long-wavelength spectrometer (LWS), a photo-polarimeter (PHT), and a short-wavelength spectrometer (SWS). The instruments jointly covered wavelengths from 2.5 to around 240 microns with spatial resolutions ranging from 1.5 arcseconds to 90 arcseconds. Its 60 cm diameter telescope was cooled by
superfluid liquid helium to temperatures of 2-4 K. The mission was a great technical, operational and scientific success. During its routine operational phase, ISO successfully made some 30,000 individual imaging, photometric, spectroscopic, and polarimetric observations ranging from objects in our own solar system to the most distant extragalactic sources.

See also: → infrared; → space; → observatory.

Observing a large area of sky (or the whole sky) in infrared wavelengths.

See also: → infrared; → survey.

A telescope capable of observing → infrared radiation from astronomical objects.

See also: → infrared; → telescope.

A range of infrared wavelengths to which the Earth’s atmosphere is relatively transparent, and at which observations can be made from the ground. Infrared windows are found near wavelengths of 1.25, 1.65, 2.2, 3.6, 5.0, 10, 20, and 30 microns, and beyond 300 microns.

See also: → infrared; → window.

A sound wave whose frequency is below the audible range of about 20 → Hz to 20,000 Hz. → sound wave; → ultrasound; → subsonic.

See also: → infra- + → sound.

That which enters into a → compound or → mixture.

Etymology (EN): M.E., from L. ingredient- (nominative ingrediens) “that which enters into,” p.p. of ingredi “to go in, enter,” from → in- + gradi “to go, to walk,” → egress.

Etymology (PE): Darâné, literally “brought into,” from dar-, → in-, + ân present stem of ânidan “to bring, to lead,” → relate, + nuance suffix -é.

Same as → immersion.

See also: From → in- + gress, → egress.

To take or receive (property, a right, a title, etc.) by succession or will, as an → heir (Dictionary.com).

See also: → heritage.

1. Capable of being inherited.
   

2. Capable of inheriting; qualified to inherit (Dictionary.com).

See also: → inherit; → -able.

1. Something that is or may be inherited; property passing at the owner’s death to the heir or those entitled to succeed; legacy; something, as a quality, characteristic, or other immaterial possession, received from progenitors or predecessors as if by succession.
   

2. The genetic characters transmitted from parent to offspring, taken collectively.
   

3. The act or fact of inheriting by succession, as if by succession, or genetically (Dictionary.com).

See also: Verbal noun of → inherit.

A person who → inherits; → heir.

See also: → inherit; → -or.

The condition or an instance of not being homogeneous.

See also: → in- “not” + → homogeneity.

Lack of homogeneity; something that is not → homogeneous.

See also: → in- “not” + → homogeneous.

Of, pertaining to, or occurring at the beginning.

Etymology (EN): Initial, from L. initialis, from initium “a beginning, an entrance,” from p.p. stem of inire “to go into, begin,” from → in- + ire “to go,” → ion.

Etymology (PE): Âqâzin “pertaing to the beginning,” from âqâz “beginning,” from Proto-Iranian *āgāza-, from prefix ā-

• *gāz- “to take, receive,” cf. Sogdian āγāz “beginning, start,” pcγz “reception, taking.”

1. Conditions at an initial time t = t₀ from which a physical system or a given set of mathematical equations evolves.
   

2. Meteo.: A prescription of the state of a → dynamical system at a specified time; for all subsequent times, the → equation of motion and → boundary conditions determine the state of the system.

See also: → initial; → condition.

The mass of a star at its arrival on the → main sequence.

See also: → initial; → mass.

A mathematical expression describing the relative number of stars found in different ranges of mass for a cluster of stars at the time of its formation. It is defined as φ(log M) = dN / dlog M ∝ M ^-Γ, where M is the mass of a star and N is the number of stars in a logarithmic mass interval. The value of the slope found by Salpeter (1955) for → low-mass and → intermediate-mass stars in the → solar neighborhood is Γ = 1.35. The IMF can be expressed also in linear mass units: χ(M) = dN / DM ∝ M ^-α. Note that χ(M) = (1 / M lm 10) φ(log M), and α = Γ + 1. In this formalism the Salpeter slope is α = 2.35. There is a third way for representing the IMF, in which the exponent is x = -α.
The IMF is not a single power law over all masses, from → brown dwarfs to → very massive stars (Kroupa, 2002, Science 295, 82). Different slopes have been found for different mass segments, as follows: α = 1.3 for 0.08 ≤ M_solar < 0.5; α = 2.3 for 0.5 ≤ M_solar < 1; α = 2.3 for 1 ≤ M_solar.
The IMF at low masses can be fitted by a → lognormal distribution (See Bastian et al., 2010, ARAA 48, 339 and references therein). See also → canonical IMF.

See also: → initial; → mass; → function.

The value of the phase corresponding to the origin of time. Same as the → epoch angle.

See also: → initial; → phase; → angle.

An instant of infinite density, infinite pressure, and infinite temperature where the equations of general relativity break down, if the standard Big Bang theory is extrapolated all the way back to time zero.
→ singularity.

See also: → initial; → singularity.

1. The first step or action of a matter; commencing move.
   

   2. An introductory act or step; leading action.

Etymology (EN): From Fr. initiative, from L. initiatus, p.p. of initiare “to begin,” from initium “a beginning,” → initial.

Etymology (PE): Bongâm, from bon “basis; root; foundation; bottom,” → fundamental, + gâm “step, pace,” → egress.

1. General: To force into a passage, cavity, or tissue.
   

2. Math.: Verbal form related to → injection.

Etymology (EN): From L. injectus, p.p. of injicere “to throw in or on,” from → in- “in” + -icere, combining form of jacere “to throw.”

Etymology (PE): Daršândan, from darešândan, from dar-, → in, +
ešândan, → eject.

1. General: The act of injecting. Something that is injected.
   

2. Physics: The process of introducing electrons or holes into a semiconductor so that their total number exceeds the number present at thermal equilibrium. → hole injection.
   

3. Math.: A one-to-one → mapping. In other words, a mapping from a → set A onto a set B such that for every element in B there is at the most an element in A.

See also: Verbal noun of → inject.

Of or pertaining to a → injection.

See also: Adj. related to → injection.

A small arm of the sea, a lake, or a river.

Etymology (EN): From → in- + let “to allow,” M.E. leten, O.E. lætan; cognate with Du. laten, Ger. lassen, akin to Gk. ledein “to be weary”, L. lassus “tired.”

Etymology (PE): Šâxâbé, literally “branch of water,” from šâx, → branch, + âb “sea, river, → water” + noun suffix -é.

Situated within or farther within; interior.

Etymology (EN): From O.E. inra, comparative of inne (adv.) “inside;” → in-.

Etymology (PE): Daruni, adj. of darun “in, into; within” (Mid.Pers. andarôn
“inside,” from andar, → inter-, + rôn “side, direction;” Av. ravan- “(course of a) river”).

The central part of the → Earth’s core, composed of solidified → iron and → nickel, and
extending from a depth of about 5100 km to the center of the Earth, at 6360 km. Its radius is about 1/3 that of the whole core and is effectively decoupled from the → mantle due to the molten nature of the surrounding → outer core. The radius of the inner core is defined by a small increase in → compressional wave velocity at a radius of about 1200 km. Its density is about 12 g/cm³. The → temperature of the inner core has been estimated at 5000-7000 °C.

See also: → inner; → core.

A → near-Earth object whose → orbit lies always inside Earth’s orbit.

See also: → inner; → Earth; → object.

One of the five → Lagrangian points, denoted L1, which lies between the two bodies on the line passing through their center of mass. In a → close binary star system mass transfer occurs through this point.

See also: → inner; → Lagrangian points.

A → Lindblad resonance expressed by: Ω_p = Ω - κ/m.

See also: → inner; → Lindblad resonance.

The planets Mercury, Venus, Earth and Mars collectively. T hey are also known as the terrestrial planets.

See also: → inner; → planet.

The smallest → circular orbit in which a particle can stably orbit a → black hole according to → general relativity without the risk of falling past the → event horizon. In other words, the ISCO is the inner edge of the → accretion disk around a black hole. Therefore, characteristics of accretion disks depend on ISCO. The radius of ISCO is calculated to be three times the → Schwarzschild radius (3 R_Sch). ISCO is closer to event horizon for rotating black hole.

See also: → inner; → stable; → circular; → orbit.

A dynamical model developed in France since 2003 which calculates the motion of → Solar System bodies with the highest accuracy. It integrates
data obtained by NASA and ESA space missions. See, for example, A. Fienga et al. 2011, arXiv:1108.5546.

See also: INPOP, short for Intégration Numérique Planétaire de l’Observatoire de Paris; → ephemerides.

1. The current, voltage, or driving force applied to an electric or electronic circuit or device.
   
2. Computers: Data which is transferred from outer external storage elements to the internal storage of a computer. → output.

Etymology (EN): From → in- + put, from M.E. put(t)en “to push, thrust, put;” O.E. *putian.

Etymology (PE): Darundâd, from darun “in” → in-,
→ intra-, + dâd “given,” p.p. of dâdan “to give” (Mid.Pers. dâdan “to give,” O.Pers./Av. dā- “to give, grant, yield,” akin to L. data, → datum).

A catalog based on a pre-defined list of objects prepared for new observations, mainly using → space telescopes. → Ecliptic Plane Input Catalogue.

See also: → input; → catalog.

1. To mark with words, characters, etc., especially in a durable or conspicuous way.
   

2. Geometry: To draw within another figure so that the inner lies entirely within the boundary of the outer, touching it at as many points as possible: e.g. to inscribe a circle in a square.

Etymology (EN): From L. inscribere, from → in- + scribere “to write,” from PIE *skreibh- (cf. Gk. skariphasthai “to scratch an outline, sketch;” Lett. skripat “scratch, write;” 0 O.N. hrifa “scratch”); PIE base *sker- “cut, incise.”

Etymology (PE): Darveštan, darvisidan (on the model of neveštan, nevisidan “to write”),
from dar-, → in-, + vešt-, vis- (see below)

• -idan infinitive suffix. Vešt-, vis- from Mid.Pers. bišt-, bis- (nibištan, nibes- “to write”), from O.Pers. pais- “to adorn, cut, engrave,” Av. paēs- “to paint, adorn,” paēsa- “adornment,” Mid.Pers. pēsīdan “to adorn;” cf. Skt. piśáti “adorns; cuts;” Gk. poikilos “multicolored;” L. pingit “embroiders, paints;” O.C.S. pisati “to write;” O.H.G. fēh “multicolored;” Lith. piēšti “to draw, adorn;” PIE base *peik- “colored, speckled.”

An angle whose vertex lies on a circle and whose sides are chords of the circle.

See also: Inscribed p.p. of → inscribe; → angle.

1. Something inscribed; the act of inscribing.
   

   2. The entering of a name on or as if on a list.
      

   3. A historical or religious text carved on stone, brick, or other hard surface.
      

   4. A brief dedication, as of a book or a work of art.

See also: Verbal noun of → inscribe.

Not secure; exposed or liable to risk, loss, or danger.

See also: → in-; → security.

The quality or state of being insecure; something insecure.

See also: → in-; → security.

Biology: To inject → semen into the reproductive tract a female animal or plant by artificial means.

Etymology (EN): From L. inseminatus, p.p. of inseminare “to sow, implant,” from → in- + → semen “seed.”

Etymology (PE): daršosaridan, from dar-, → in-, + šosar, → semen, + -idan suffix of infinitives.

The act or process of inseminating.

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

A NASA lander designed to study the interior of the planet Mars. It will be a stationary mission, in contrast to NASA’s famous Opportunity, Spirit and Curiosity rovers. Staying in place is necessary for its major science goals, which include learning more about the Martian composition, and how tectonically active the red planet is.

InSight launched toward Mars on May 5, 2018, landed on Nov. 26, 2018, at the Martian Elysium Planitia, an equatorial zone just south of an ancient volcanic area. InSight will send back data about Mars' interior for about 1 Mars year, or 728 Earth-days.

The lander uses sophisticated instruments, to delve deep beneath the surface and seek the fingerprints of the processes that formed the terrestrial planets. It does so by carrying out → seismology, heat flow measurements, and precision tracking.

See also: InSight, short for Interior Exploration using Seismic Investigations, Geodesy and Heat Transport; → mission.

To be firm in a demand or course; refuse to yield (Dictionary.com).

Etymology (EN): L. insistere “stand upon, dwell upon,” from → in- “upon” + sistere “take a stand,” → resist.

Etymology (PE): Daristâdan “to insist” (Dehxodâ), from dar-, → in-,

• istâdan “to stand,” → resist.

The act or fact of insisting; the quality of being insistent.

See also: Verbal noun of → insist.

Earnest or emphatic in dwelling upon, maintaining, or demanding something; persistent; pertinacious (Dictionary.com).

See also: Adjective from → insist.

The amount of radiative energy received from the Sun per unit area per unit time.

Etymology (EN): Insolation, from L. insolatus p.p. of insolare “to place in the sun,” from → in- + sol, → sun,

• -ation a suffix denoting action or condition.

Etymology (PE): Xortâbgiri, from xor “sun,” cognate with L. sol→ sun + tâb “light; heat, warmth; illuminating,” from tâbidan, tâftan “to shine,” tafsidan “to become hot” (Av. tāp-, taf- “to warm up, heat,” tafsat “became hot,” tāpaiieiti “to create warmth;” cf.
Skt. tap- “to spoil, injure, damage; to suffer; to heat, be/become hot,” tapati “burns;” L. tepere “to be warm,” tepidus “warm;” PIE base *tep- “warm”) + giri verbal noun of gereftan “to take, seize” (Mid.Pers. griftan, Av./O.Pers. grab- “to take, seize,” cf.
Skt. grah-, grabh- “to seize, take,” graha “seizing, holding, perceiving,” M.L.G. grabben “to grab,” from P.Gmc. *grab, E. grab “to take or grasp suddenly;” PIE base *ghrebh- “to seize”).

1. To look carefully at or over; view closely and critically.
   

2. To view or examine formally or officially (Dictionary.com).

Etymology (EN): From L. inspectus, p.p. of inspicere “to look into,” from → in- + specere “to look,” → -scope.

Etymology (PE): Dargâsidan, from dar-, → in-, + gâsidan “to look,” → speculate.

1. The act of inspecting or viewing, especially carefully or critically.
   

2. Formal or official viewing or examination (Dictionary.com).

See also: Verbal noun of → inspect.

The inward spiraling of an orbiting → black hole toward a central → supermassive black hole (SMBH) as it radiates → gravitational wave. As a
result, the orbit decays, and the orbital period decreases, leading to the → merging of
both black holes as they get close enough. Once merged, the single hole goes through a stage called → ringdown.

See also: → in; → spiral.

The condition of a system when it is disturbed by internal or
external forces. The system continues to depart from the original condition, in contrast to a stable system, which will return to its previous condition when disturbed.

See also: From → in- “not” + → stability

A narrow, almost vertical, band on the right hand side of the → main sequence in the → H-R diagram occupied by many different types of → pulsating stars
(→ RR Lyrae, → Cepheids, → W Virginis, → ZZ Ceti). Stars traverse this region at least once after they leave the main sequence. The narrow temperature range of the instability strip corresponds to the stellar → effective temperature that can sustain → partial ionization zones, capable of maintaining stellar oscillations. The blue (hot) edge of the instability strip pertains to stars with surface temperatures hotter than ~ 7500 K. Because these stars have partial ionization zones too close to their surface, the pulsation mechanism is not active. The red (cooler) edge of the instability strip is determined by stars with a temperature lower than ~ 5500 K. In these stars convection prevents the build-up of heat pressure necessary to drive pulsations.

See also: → instability; → strip.

1. To place in position or connect for service or use.
   

2. To establish in an office, position, or place (Dictionary.com).

Etymology (EN): From M.L. installare, from L. → in- + M.L. stallum “stall,” from a Germanic source (compare O.H.G. stal “standing place, stand, place, stable, stall,” Ger. Stall “stable,” Stelle “place”), from PIE root *stel- “to put, stand;” cf. Gk. stele “standing block, slab,” stellein “to set in order, arrange, array, equip, make ready.”

Etymology (PE): Darhidan, literally “to place in,” from dar “in, into,” → in-, + -hidan present stem of (ne)hâdan “to put, place, establish” → position.

1. Something installed, as machinery or apparatus placed in position or connected for use.
   

2. The act of installing.
   

3. The fact of being installed (Dictionary.com).

See also: → install; → -tion.

1. A case or occurrence of anything.
   
2. An example put forth in proof or illustration (Dictionary.com).

Etymology (EN): M.E., from O.Fr. instance, from L. instantia “presence; earnestness, urgency,” literally “a standing near,” from instans, → instant.

Etymology (PE): Seté, from set, present stem of setâdan, variant of istâdan “to stand,” → standard, + -é noun suffix.

1a) An → infinitesimal or very short space of time;  a → moment.

1b) The point of time now present or present with reference to some action or even.

2a) Succeeding without any interval of time; prompt;  → immediate.

2b) Occurring, done, or prepared with a minimal amount of time and effort; produced  rapidly and with little preparation (Dictionary.com).

Etymology (EN): M.E., from O.Fr. instant (adj.) “assiduous, at hand,” from M.L. instans-, in classical L. “present, pressing, urgent,” literally “standing near,” pr.p. of instare “to urge, to stand near, be present,” → insist.

Etymology (PE): 1) Lahzé, from Ar. laHZat, laHZa “glance; moment.”
2) Setand (variant of istandé), from setâdan, variant of istâdan “to stand,” → instance.

1. Occurring, done, or completed in an instant.
   

   2. Existing at or pertaining to a particular instant (Dictionary.com).

See also: → instant; → -an; → -eous.

The → acceleration of a particle at time t defined by a = lim Δv/Δt = dv/dt. It is the limiting value of Δv/Δt at time t as both Δv and Δt approach zero.

See also: → instantaneous; → acceleration.

The velocity of a particle at some one instant of time, or at some one point of its path. It can be defined as the limiting value of the average velocity when the second point is taken closer and closer to the first point.

See also: → instantaneous; → velocity.

The arched upper surface of the human foot between the toes and the ankle (Dictionary.com).

Etymology (EN): → in-; → step.

Etymology (PE): Ruyé, → surface; pâ, → foot.

To provoke, urge, or incite.

Etymology (EN): From L. instigatus, p.p. of instigare “to urge on, incite,” from → in- “in” + *stigare
“to prick,” from PIE root *steig- “to prick, stick, pierce,” cognate with Pers. tig, tiz, → sharp.

Etymology (PE): Âqâlidan “to excite, rouse.”

The act of instigating; incitement.

See also: Verbal noun of → instigate.

1. An object used for producing music.
   

2. A measuring device designed to record the present value of a quantity under observation.

Etymology (EN): From O.Fr. instrument, from L. instrumentem “a tool, apparatus, furniture,” from instruere “to arrange, furnish,” from → in- + struc- (var. s. of struere “to put together”) + -tus p.p. suffix.

Etymology (PE): 1) Sâz “(musical) instrument; apparatus; harness; furniture,” from sâzidan, sâxtan “to build, make, fashion; to adapt, adjust, be fit” (from Mid.Pers. sâxtan, sâz-, Manichean Parthian s’c’dn “to prepare, to form;” Av. sak- “to understand, to mark,” sâcaya- (causative) “to teach”).

2. Sâzâl, from sâz + -âl, → -al.

The correctable part of the inaccuracy of a measuring instrument.

See also: → instrument; → error.

Of, relating to, or performed by or with one or more instruments.
See also:
→ instrumental broadening, → instrumental flexure, → instrumental magnitude, → instrumental profile, → instrumental response function, → instrumentalism, → instrumentalist.

See also: Adj. of → instrument.

The broadening of a point source caused by the response functions of the telescope and the instrument used.

See also: → instrumental; → broadening.

An image defect caused by the mechanical flexure of materials; for example the curved-shape image of a long slit in a spectrograph.

See also: → instrumental; → flexure.

The magnitude derived directly using → Pogson’s relation. The instrumental magnitude depends on → detector→ sensitivity, telescope → aperture, exact filter → bandpass, etc. It must be → calibrated to some standard → photometric system.

See also: → instrumental; → magnitude.

The shape of instrument’s response to the input signal. The Fourier transform of the source function by the instrument function.

See also: → instrumental; → profile.

The mathematical form of the way an instrument affects the input signal.

See also: → instrumental; → response; → function.

In the philosophy of science, the pragmatic view that a scientific theory is no more than a useful instrument or tool for getting our experiences in some order.

See also: → instrumental; → -ism.

An astronomer, engineer, or technician who is concerned with the construction of astronomical instruments.

See also: → instrumental + → -ist.

1. The design and use of scientific instruments for detection, measurement, control, computation, and so on.
   

2. The ensemble of instruments contained in a given machine or system.

Etymology (EN): From → instrument + -ation a combination of -ate and -ion, used to form verbal nouns.

Etymology (PE): Sâzâlgari, noun from sâzâlgar, → instrumentalist. Sâzâlgân, with plurality suffix -gân.

To cover or to separate from conducting bodies by means of nonconductors so as to prevent or reduce the passage, transfer, or leakage of heat, electricity, or sound. → insulation, → insulator.

Etymology (EN): From L. insulatus “made into an island,” from L. insula “island.”

Etymology (PE): From âyeq, → insulator, + kardan “to do,” → -or.

1. The act or fact of insulating.
   

2. Any material used to reduce or prevent the transfer of electricity, heat, cold, or sound.

See also: Verbal noun from → insulate.

1. A material or an object that does not easily allow heat, electricity, light, or sound to pass through it.
   

2. Electricity: A material, such as glass or porcelain, that opposes a very high resistance to the passage of an electric current so that the flow of current through it is negligible; a nonconductor.
   

3. One who, or that which, insulates.

Etymology (EN): Agent noun from → insulate + → -or.

Etymology (PE): Âyeq, loan from Ar.

The act, system, or business of insuring property, life, one’s person, etc., against loss or harm arising in specified contingencies, as fire, accident, death, disablement, or the like, in consideration of a payment proportionate to the risk involved (Dictionary.com).

Etymology (EN): → insure; → -ance.

Etymology (PE): Bimé, from bim “fear, danger” (variant bâk “fear, hesitation”);
Mid.Pers. bīm “fear, fright, dread;” Av. b(a)ii- “to fear;” cf. Skt. bhayⁱ- “to fear,” bhīmá- “terrible;” Lith. bijoti(s), Latv. bîtiês “to fear, be afraid;” O.H.G. biben “to shiver;” PIE *b^heiH₂- “to fear” (Cheung 2007).

1. To provide or obtain → insurance on or for.
   

2. Make certain that something is definitely so. Same as make sure and ensure.

Etymology (EN): Variant of → ensure.

Etymology (PE): 1) Bimé kardan, from bimé, → insurance,

• kardan “to do, make,” → -ize.
  

2. Dartenzidan, from dar-, → in-,

• tenz, → sure, + -idan infinitive suffix, → -ize.

Same as → integer number.

Etymology (EN): From L. integer “whole,” literally “intact, untouched,” from → in- “not” + root of tangere “to touch.”

Etymology (PE): Doroste, from dorost “whole, complete; healthy; right,” → integral.

Any member of the set consisting of → positive and → negative whole numbers and → zero. Examples: -5, -2, -1, 0, 1, 2, 5.

See also: → integer; → number.

An expression of an integer nas the sum of one or more positive integers. The number of different partitions of n is denoted p(n). This function is called the partition function. For example, p(5) = 7, because 5 can be partitioned as: 5 = 5 = 4 + 1 = 3 + 2 = 3 + 1 + 1 = 2 + 2 + 1 = 2 + 1 + 1 + 1 = 1 + 1 + 1 + 1 + 1.

See also: → partition; → integer.

1. Consisting of whole numbers or integers.
   
2. Mathematical function obtained by the process of → integration.

Etymology (EN): Integral, from M.Fr. intégral, from M.L. integralis “forming a whole,” → integer “whole.”

Etymology (PE): 1) Dorostâl, from dorost “whole, complete; healthy; right,” related to dorud “benediction, praise, thanksgiving,” from
Mid.Pers. drust “whole; healthy; well, right,” drôd “health, thriving;” O.Pers. duruva- “firm, certain, immune;” Av. druua- “healthy;” cf. Skt. dhruvá- “fixed, firm, immovable, lasting, certain;” Russ. zdorovyjj “healthy;” See also → sound.

2. Dorostâl, from dorost + -âl, → -al.

Branch of the calculus that deals with integration and its use in finding volumes, areas, equations of curves, solutions of differential equations, etc.

See also: → integral; → calculus.

An equation involving an unknown function that appears as part of an integrand.

See also: → integral; → equation.

A technique in spectroscopy for recording a spectrum from
each point of an extended object. The field of view image is divided into a multitude of small components using different methods, e.g. lenslet arrays, fiber bundles, or image slicers. From each component a spectrum is extracted or an image is reconstructed at a particular wavelength.

See also: → integral; → field; → spectroscopy.

A function whose image is a subset of the integers, i.e. that takes only integer values.

See also: → integral; → function.

Math.: An operator whose inverse is a differential operator.

See also: → integral; → operator.

The function which is being integrated in a given integral.

Etymology (EN): From L. integrandum, noun use of neuter of integrandus, gerundive of integrare, → integrate.

Etymology (PE): Dorostâlân, pr.p. of dorostâlidan, → integrate.

1. To carry out the mathematical operation of → integration.
   

2. To add up photons when exposing a detector to incoming light through the telescope.

Etymology (EN): From L. integratus p.p. of integrare “to renew, restore,” → integer + -ate a verb forming suffix.

Etymology (PE): Dorostâlidan, infinitive of dorostâl, → integral; dorostâl gereftan “to take (an) integral;” gereftan
“to take, seize” (Mid.Pers. griftan, Av./O.Pers. grab- “to take, seize,” cf.
Skt. grah-, grabh- “to seize, take,” graha “seizing, holding, perceiving,” M.L.G. grabben “to grab,” from P.Gmc. *grab, E. grab “to take or grasp suddenly;” PIE base *ghrebh- “to seize”).

A circuit whose components are found on a single semiconductor substrate.

See also: Integrated, p.p. of → integrate; → circuit.

The branch of electronics that deals with integrated circuits, especially the interdependence of material, circuits, and design.

See also: Integrated, p.p. of → integrate; → electronics.

The magnitude an extended object (nebula, galaxy,etc.) would have if all of its light were concentrated into a point source

See also: Integrated, p.p. of → integrate; → magnitude.

A function that converts a → differential equation, which is not exact, into an → exact differential equation. This is done by multiplying all terms of the original equation by the integrating factor.

See also: → integrate; → factor.

In calculus the operation which consists of finding the areas enclosed by curves through the summations of infinitesimals. The inverse process of differentiation.

See also: Verbal noun of → integrate.

The time during which a detector integrates the incoming photons.

See also: → integration; → time.

1. The → power or faculty of the → mind by which one knows or → understands, as distinguished from that by which one feels and that by which one wills; the understanding; the faculty of thinking and acquiring → knowledge.
   

2. Capacity for thinking and acquiring knowledge, especially of a high or complex order; mental capacity.
   

3. A particular mind or → intelligence, especially of a high order.
   

4. A person possessing a great capacity for → thought
   and knowledge.
   

5. Minds collectively, as of a number of persons or the persons themselves (Dictionary.com).

Etymology (EN): M.E., from O.Fr. intellecte “intellectual capacity,”
from L. intellectus “discernment, understanding,” from intelligere “to understand, discern,” from → inter- “between” + legere “to choose, pick out, read.”

Etymology (PE): From hôš, huš “intellect, understanding; mind;” Mid.Pers. hôš; Av. uši-
“intelligence, understanding; mind,” uši.darθra- “holding in mind;” + suffix -an.

1a) Appealing to or engaging the → intellect.

1b) Of or pertaining to the intellect or its use.

1c) Possessing or showing intellect or mental capacity, especially to a high degree: an intellectual person.

1d) Guided or developed by or relying on the intellect rather than upon emotions or feelings; rational.

1e) Characterized by or suggesting a predominance of intellect.

1f) (n.) A person of superior intellect.

1g) A person who places a high value on or pursues things of interest to the intellect or the more complex forms and fields of knowledge, as aesthetic or philosophical matters, especially on an abstract and general level.

1h) An extremely rational person; a person who relies on intellect rather than on emotions or feelings.

2. A person professionally engaged in mental labor, as a writer or teacher (Dictionary.com).

Etymology (EN): From L. intellectualis, → intellect + → -al.

Etymology (PE): Hošanvâr with suffix -vâr denoting suiting, befitting, resembling, in the manner of, possession (as in omidvâr, ayâlvâr, râhvâr).

A property of the mind that encompasses many related abilities, such as capacity for learning, reasoning, understanding, and similar forms of mental activity.
Machines: The ability of a device, program, or system to solve problems more automatically or more skillfully than competitive systems.

Etymology (EN): From O.Fr. intelligence, from L. intelligentia “understanding,” from intelligentem (nom. intelligens) “discerning,” pr.p. of intelligere “to understand, comprehend,” from → inter- “between” + legere “choose, pick out, read;” PIE base *leg- “to pick together, gather, collect;” cf. Gk. legein “to say, tell, speak, declare,” originally, in Homer “to pick out, select, collect, enumerate;” lexis “speech, diction;” logos “word, speech, thought.”

Etymology (PE): Huš, from Mid.Pers. hôš “intellect, understanding; mind,” from Av. uši- “intelligence, understanding; mind,” uši.darθra- “holding in mind.”

1. Possessing intelligence; having the faculty of → understanding and → reasoning.
   

2. Computer science: Having → memory and → processor to modify action in response to ongoing events.

See also: Back formation from → intelligence.

Existing or occurring in a high or extreme degree. See also → tense.

Etymology (EN): From M.Fr. intense, from L. intensus “stretched, strained, tight,” originally p.p. of intendere “to stretch out, strain,” from in- “toward” + tendere “to stretch;” from PIE base *ten- “to stretch;” cf. Pers. tanidan “to spin, twist, weave,” as below.

Etymology (PE): âtanu, from â- affirmative prefix + tanu “stretched, strained,” from tan + -u suffix of excess. The middle element tan, from tanidan
“to spin, twist, weave” (Mid.Pers. tanitan; Av. tan- to stretch, extend;" cf. Skt. tan- to spin, stretch;" tanoti “stretches,” tantram “loom;” Gk. teinein “to stretch, pull tight;” L. tendere “to stretch;”
PIE base *ten- “to stretch”), Pers. târ “string,” tân “thread,” tur “fishing net, net, snare,” and tâl “thread” (Borujerdi dialect) belong to this family; variants tanta “cobweb,” tanadu, tafen, kartané, kârtané, kâtené,
Pashtu tanistah “cobweb;” cf. Skt. tantu- “cobweb, thread, string”).

The action of making or becoming stronger or more extreme.

See also: verbal noun of → intensify.

1. Something that intensifies.
   

2. Substance used to increase the density or contrast of an image on a photographic film or plate.

See also: Agent noun of → intensify.

To make intense or more intense.
To increase the density and contrast of a photographic image by chemical treatment.

Etymology (EN): From → intense + -ify variant of -fy after a consonant, from O.Fr. fier, from L. -ficare “to do, make.”

General: The quality or condition of being intense.
Physics: Strength, as of energy or a force per unit of area, solid angle, time, etc.; e.g. → electric intensity; → magnetic intensity.

Etymology (EN): From → intense + → -ity.

Etymology (PE): Dartanuyi state, condition noun of dartanu, → intense.

The height of a spectral line above the continuum base.

See also: → intensity; → line.

The rate of emitted energy from unit surface area through unit solid angle. The radiation from a surface has different intensities in different directions.

See also: → intensity; → radiation.

1. Of, pertaining to, or characterized by intensity.
   

2. Tending to intensify; intensifying.
   

3. Requiring or having a high concentration of a specified quality or element (used in combination).
   

4. Grammar: Indicating increased emphasis or force. “Certainly” is an intensive adverb. “Myself,” in I did it myself, is an intensive pronoun (Dictionary.com).

See also: → intense; → -ive.

A prefix that highly emphasizes roots of words to which it is attached. In other words, intensive prefixes heighten the force of the primary meanings of words. These prefixes can effectively be translated as “thoroughly” to highlight their intensive function. For example the prefixes → re-, → de-, and → com-.

See also: → intensive; → prefix.

A prefix denoting “between, among, mutually, reciprocally.”

Etymology (EN): Inter-, from L. inter (prep., adj.) “among, between,” from PIE *enter “between, among” (cf. Pers. andar-, as below; Skt. antár; Gk. entera (pl.) “intestines,” O.Ir. eter; O.Welsh ithr “among, between;” O.H.G. untar;
O.E. under “under”), from en- “in” + -ter comparative suffix.

Etymology (PE): Mod.Pers. andar “in, into, within” (added to the words pedar “father,” mâdar “mother,” barâdar “brother,” xâhar “sister,” it implies “step-father, step-mother, half-brother, half-sister” respectively), from Mid.Pers. andar “in, among, concerning;” O.Pers. anatr, Av. antarə’ (adv., prep., prev.), antarə (adv., prev.), “inside, intra, within, between;” also Av. antara- (adj.) “interior;” cf. Skt. ántara- “interior, adjacent to; intimate, dear;” from PIE *enter, as above.
The Av. antarə’ is used with verbal stems to create abstract actions. For example,
antarə’-mruyē “to prohibit,” from antare- “inter-” + mruyē “to speak,” from root mrū- “to speak, say.” This is exactly the same pattern as L. inter-dicere “to interdict, forbid, prohibit,” from inter-, as above,

• dicere “to speak.” The Av. antare- is used with another verb to produce the same sense: antarə-uxti “to interdict,” from antarə- + uxti “to speak, to say.” E. Benveniste (1975) made an interesting investigation on the origin of the “to speak inside” paradigm for the concept of interdiction. He argues that inter- derives in fact from *en-ter,
  the second component, while being a comparative form, introduces the notion of separation. His conclusion is that antarə-mruyē
  or inter-dicere mean “to pronounce inside (a group) so as to separate (or isolate somebody).” According to Benveniste, the Av. terms are the oldest forms in the Indo-European languages which convey an important piece of information about an aspect of Indo-European life/tradition in pre-historic times.

To act upon one another; have a mutual or reciprocal action.

See also: Interact, from → inter- + → act.

A binary star system in which mass transfer between the components takes place. → contact binary; → Roche lobe.

See also: Interacting, adj. of → interact;
→ binary.

Galaxies that are close enough for their mutual gravitational attraction to produce perturbed shapes or extruded filaments of stellar material, called → tidal tails. Most galaxies are in clusters, and gravitational interactions
between them are common.

See also: Interacting, adj. of → interact;
→ galaxy.

General: Mutual or reciprocal action or influence.
Physics: 1) What happens between a system and its surroundings when an observable change in one corresponds to or correlates with an observable change in the other.

2. The natural phenomenon of the transfer of energy between two particles. The
   four known kinds of interactions, in the order of increasing strength, are: → gravitational, → weak, → electromagnetic, and → strong.

See also: Interaction, from → inter-; + → action.

Capable of acting on or influencing each other

See also: From → interaction; + → -al.

1. Acting one upon or with the other.
   

2. Computers: Of or pertaining to a system or program that maintains an exchange with the user, alternately accepting input and then responding.

See also: → inter-; → active.

A low-density region separating the spiral arms of a galaxy.

Etymology (EN): Interarm, from → inter- + arm “body part,” from
O.E. earm “arm,” from P.Gmc. *armaz (cf. M.Du., Ger. arm, O.N. armr, O.Fris. erm), from PIE base *ar- “to fit, join;”
Mod.Pers. arm “arm, from the elbow to the shoulder;” Av. arma-, arəmo- “arm;” Skt. irma- “arm;”
Gk. arthron “a joint,” L. armus “shoulder;” → region.

Etymology (PE): Andarbâzu, from andar-, → inter-, + bâzu “arm,” from
Mid.Pers. bâzûk “arm;” Av. bāzu- “arm;” cf. Skt. bāhu- “arm, forearm;” Gk. pechys “forearm, arm, ell;”
O.H.G. buog “shoulder;” Ger. Bug “shoulder;” Du. boeg; O.E. bôg, bôh “shoulder, bough;” E. bough " a branch of a tree;" PIE *bhaghu- “arm”); nahiyé, → region. Andararm, from andar-, → inter-, + arm, as above.

Between atoms; relating to the interaction of different atoms.

See also: → inter-; → atomic.

Adj. of → intercalation; having such a day or month inserted. → bissextile.

Etymology (EN): From L. intercalarius, from ntercal(are)→ intercalate + -arius “-ary.”

Etymology (PE): Andarheli adj. of andarhel, → intercalate.

To insert (an extra day, month, etc.) in the calendar to make it follow the seasons or moon phases.

Etymology (EN): From L. intercalatus p.p. of intercalare “to proclaim the insertion of an intercalary day or month,”
from → inter- + calare “to proclaim, announce solemnly;” → calendar.

Etymology (PE): Andarhelidan, andarheštan “to insert,” from andar-→ inter- + helidan, heštan “to place, put” from Mid.Pers. hištan, hilidan “to let, set, leave, abandon,” Parthian Mid.Pers. hyrz; O.Pers. hard- “to send forth,” ava.hard- “to abandon;”
Av. harəz- “to discharge, send out; to filter;” hərəzaiti “releases, shoots;” cf. Skt. srj- “to let go or fly, throw, cast, emit, put forth;” Pali sajati “to let loose, send forth.”

The act of intercalating; insertion. Something that is intercalated.
Astro.: An insertion into a calendar, → intercalate.
Geology: The presence of a body of rock interbedded with another body of different rock.

See also: The verbal noun of → intercalate.

A medium in which several molecular clouds are situated.

See also: → inter- + → cloud + → medium.

The diffuse medium between → clumps inside → molecular clouds.

See also: → inter- + → clump + → medium.

The matter lying between the clusters of galaxies in an aggregation of such clusters.

See also: → inter- + → cluster

• → medium.

To be or become connected reciprocally.

See also: → inter- + → connect.

Reciprocal connection between two or several things.

See also: → andar-; → connection.

In spectroscopy, same as → semi-forbidden line.

See also: → interconnection; → line.

Of an approach or study that integrates content, data, methods, tools, concepts, and theories from two or more disciplines or bodies of specialized knowledge in order to advance fundamental understanding, answer complex questions, and solve problems that are too broad or complex for a simple approach. See also → multidisciplinary and
→ transdisciplinary (Thompson Klein, J. 2010, Creating Interdisciplinary Campus Culture, John Wiley and Sons, Inc.).

See also: → inter-; → disciplinary.

1a) The sense of curiosity about or concern with something or someone.

1b) Something in which one is interested.

1c) A right, share, or claim in a business or property.

2. To engage or excite the attention or curiosity of.

Etymology (EN): M.E., from M.L. from L. interest “it concerns,” from M.L. interesse “compensation for loss,” noun use of L. interesse “to concern, make a difference, be of importance,” literally “to be between,” from → inter- “between” + esse “to be,”
→ entity.

Etymology (PE): Andarast, coined (Adib-Soltani) on the model of the L. word, as above, from andar “between,” → inter-, + ast variant hast “is, exists,” → entity.

Having an interest in something; having the attention engaged; being affected or involved.

See also: P.p. of → interest.

Inspiring interest, holding the attention.

See also: Adj. from → interest.

1. General: A surface regarded as the common boundary of two bodies, or two parts of a system, whether material or non-material.
   

2. Astro.: The intersection zone between a hot → H II region and its → associated molecular cloud.
   

3. Chemistry: The area where two immiscible phases of a dispersion come into contact.
   

4. Computers: A mechanical equipment or logical program that communicates information from one system of computing devices or programs to another.

See also: → inter- + → face.

Physics: To cause → interference.

Etymology (EN): Interfere, from M.Fr. entreferer “to strike each other,” from entre, → inter-, + ferir “to strike,” from L. ferire “to knock, strike.”

Etymology (PE): Andarzadan, from andar, → inter-, + zadan “to strike, beat,” from Mid.Pers. zatan, žatan; O.Pers./Av. jan-, gan- “to strike, hit, smite, kill” (jantar- “smiter”); cf.
Skt. han- “to strike, beat” (hantar- “smiter, killer”);
Gk. theinein “to strike;” L. fendere “to strike, push;” Gmc. *gundjo “war, battle;” PIE *g^when- “to strike, kill.”

The phenomenon occurring when two or more waves of the same → frequency having a constant → phase difference traverse simultaneously in the same region of a medium and cross each other. In the region of superposition, the the resulting wave intensity is different from the sum of intensities due to individual waves at that point. This phenomenon proved the validity of the wave theory of light.
See also → constructive interference, → destructive interference, → interference fringe, → Young’s experiment, → wave theory of light.

Etymology (EN): Interference, from → interfere + -ence a noun suffix equivalent to -ance, corresponding to the suffix -ent in adjectives.

Etymology (PE): Andarzaneš, verbal noun of andarzadan, → interfere.

A filter that uses the phenomenon of optical interferences between plane-parallel semi-transparent reflectors to transmit light selectively over a narrow wavelength band.

See also: → interference; → filter.

One of the alternating bright or dark bands produced by optical interference.

See also: → interference; → fringe.

→ order of interference.

See also: → interference; → order.

A wave pattern that results when two or more waves interfere with each other, generally showing → interference fringes. In acoustics, the interference pattern appear as the effect of → beats.

See also: → interference; → pattern.

1. Physics: A device that divides a beam of light into a number of beams and re-unites them to produce → interference. → Fabry-Perot interferometer; → Michelson interferometer.
   

2. Astro.: An arrangement of two or more separate telescopes placed at some distance from one another, each one receiving electromagnetic radiation (optical, infrared, or radio) from a celestial object and brought together to form an interference pattern.

Etymology (EN): Interferometer, from interfer, → interfer, + -o- a connective/euphonic infix + → -meter.

Etymology (PE): Andarzanešsanj, from andarzaneš→ interference + -sanj, → -meter.

Of or relating to → interferometry.

See also: → interferometer; → -ic.

A system of several telescopes coupled together in a particular configuration to carry out → interferometry.

See also: → interferometric;
→ array.

An observational technique based on principles of → interferometry.

See also: → interferometric; → technique.

1. The technique and study of the → interference phenomenon produced by → coherent electromagnetic waves.
   
2. Astro.: An observational technique that uses the interference phenomenon to substantially increase the → resolving power of telescopes.

See also: Interferometry, from interfer, → interfer, + -o- a connective/euphonic infix + → -metry.

Of, existing, or occurring in the space between galaxies. → intergalactic absorption, → intergalactic cloud, → intergalactic matter , → intergalactic medium , → warm-hot intergalactic medium.

See also: → inter-; → galactic.

→ Absorption features in the spectra of bright sources like → quasars attributed to a tenuous matter filling the medium between galaxies.

See also: → intergalactic; → absorption.

→ Intergalactic matter in the form of clouds.

See also: → intergalactic; → cloud.

Very low density material found indirectly in the space between galaxies. → intergalactic absorption.

See also: → intergalactic; → matter.

The matter or environment between the galaxies of a → cluster.

See also: → intergalactic; → medium.