An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

1) The smallest whole number, symbol 1; unity. The → multiplicative identity for real and complex numbers.
2) Being or amounting to a single unit or individual or entire thing, item, or object rather than two or more; a single.

O.E. an, from P.Gmc. *ainaz (cf. O.N. einn, Dan. een, O.Fris. an, Du. een, Ger. ein, Goth. ains), PIE base *oinos, cognate with Pers. yek, as below.

Yek "one, alone," from Mid.Pers. êwak, êv, yak, êk; cf. Baluci hivak "one, single" (Proto-Iranian *aiua-ka-); O.Pers. aiva- "one, alone;" Av. aēuua- "one, alone;" Skt. éka- "one, alone, single;" Gk. oios "alone, lonely;" L. unus "one;" E. one.

A hypothetical flow in which all the flow parameters may be expressed as functions of time and one space coordinate only. This single space coordinate is usually the distance measured along the center-line of some conduit in which the fluid is flowing (B. Massey, Mechanics of Fluids, Taylor & Francis, 2006).

→ one; → dimensional; → flow.

A → magnetohydrodynamics treatment in which the → plasma consists only of one particle species and moves with the bulk speed. The thermal motion of the particles is neglected and thus there is no motion of particles relative to each other.

→ one; → fluid; → magnetohydrodynamics.

A relationship between two distinct sets of elements such that every member of the first set can be paired with a unique element in the second set; and every member of the second set can be paired with a unique element in the first set. Two sets so related are said to be isomorphic.

→ one; → correspondence.

A plant, Allium cepa, of the amaryllis family, having an edible, succulent, pungent bulb (Dictionary.com).

M.E., from Anglo-French union, O.Fr. oignon "onion," from L. unio-, also "pearl," literally "one, unity;" sense connection is the successive layers of an onion.

Mid.Pers. payâz, payâc; cf. Sogd. piyâk "onion," Yidgha piq, Vakhi piûk, Yazghulami piyeq, Kurd. pivaz; maybe related to PIE *peuk- "to prick, to sting, to stab," because of its pungent taste; cf. Gk. peukos "sting, prick, cusp, peak."

An adverb meaning without others or anything further; alone; solely; exclusively. → if and only if.

M.E., from O.E. anlic, from ân, → one.

Ivâz, from Mid.Pers. êvâz/êvâc, from Proto-Iranian *aiua-ka-; cf. Pers. yek, → one.
Tanhâ "only," from Mid.Pers. tanihâ "alone," literally "by one person," from tan "body, person;" Av. tanu- "body, person;" cf. Skt. tanu- "body, person;" perhaps related to Proto-Iranian *tan-, PIE root *ten- "to extend, stretch," → tension.

1) Classical philosophy: That part of metaphysics which is concerned with the nature of existence or the essence of things.
2) Contemporary philosophy: The conceptions of existence in general, such as those dealt with in various versions of existentialism.
3) Informatics: A description of knowledge as a set of concepts within a domain and the relationships that can exist between those concepts. An ontology is designed for the purpose of enabling knowledge sharing and reuse.

From Mod.L. ontologia, from Gk. on (genitive ontos) "being" (pr.p. of einai "to be"), akin to L. esse "to be;" Pers. hastan, astan "to be," hasti "existence, being," as below; + -logia, → -logy.

Hasti-šenâsi, from hasti "existence," from hastan "to be," → entity, + -šenâsi, → -logy.

Two parameters, denoted A and B, that describe the major features of our Galaxy's differential rotation in the Sun's neighbourhood. A is one-half of the shear and equal to +14.4 ± 1.2 km s^-1 kpc^-1, and B, one-half of the vorticity, equal to -12.0 ± 2.8 km s^-1 pc^-1.

→ Oort cloud; → constant.

1) General: An act or instance, process, or manner of functioning or operating.
2a) Math.: A mathematical process, as addition, multiplication, or differentiation.
2b) The action of applying a mathematical process to a quantity or quantities.
3) Computers: An action resulting from a single instruction.

Verbal noun of → operate

Pertaining to a process or series of actions for achieving a result.

Adj. of → operation.

A method of mathematical analysis which in many cases makes it possible to reduce the study of differential operators, pseudo-differential operators and certain types of integral operators, and the solution of equations containing them, to an examination of simpler algebraic problems. It is also known as operational analysis.

→ operational; → calculus.

In the philosophy of science, the view that → concepts are defined in terms of measuring operations which determine their applicability. Same as operationism.

→ operation; → -ism.

1) A belief or judgment that rests on grounds insufficient to produce complete certainty.
2) A personal view, attitude, or appraisal.
3) Law: The formal statement by a judge or court of the reasoning and the principles of law used in reaching a decision of a case (Dictionary.com).

M.E., from O.Fr., from L. opinion- "opinion, conjecture; appreciation," from opinari "to think, judge, suppose," from PIE *op- "to choose."

Pažân, from Pashto pažân / pêžân, from prefix- pa-, originally *pati-, + žân variant of Pers. dân-, dânestan "to know," zân as in farzâne "intelligent, wise;" Balochi zân, Kurd. zân "to know;" cf. Sogd. patzân, Khotanese paysân- "to know;" Yidgha and Munji vəzân "to know;" Yizghulami vəzan, Yaghnobi bīzon, Sarigholi pajan, Ormuri pazán "to know;" Av. paiti-zan- "to recognize, acknowledge, appreciate;" from prefix paiti- + zan- "to know, have knowledge;" Mod.Pers. dân-, dânestan "to know," variant šenâxtan "to know, recognize," → science.

A person who is on an opposing side in a game, contest, controversy, or the like; adversary (Dictionary.com).

L. opponent-, p.p. of opponere "to oppose, to object to," literally "set against, set opposite," from op- variant of ob- before p "against" + ponere "to put, set, place," → position.

Pâdistgar, from pâdist, → opposition, + -gar, → -or.

1) The action of opposing, resisting, or combating.
2) A person or group of people opposing, criticizing, or protesting something, someone, or another group (Dictionary.com).
3) The position of a solar system body having its orbit outside that of the Earth when the Earth is in a line between the Sun and the body. At opposition the body has a solar → elongation of 180°, and is closest to the Earth. It will, in principle, be visible throughout the night. It will rise in the east as the Sun sets in the west and it will set as the Sun rises. This is because, at opposition, the body and the Sun are 12 hours apart. The inner planets can never be in opposition. The opposite of opposition is → conjunction.
4) Two periodic quantities of the same frequency are said to be in opposition when the → phase difference between them is one half of a → period.

Verbal noun of → oppose.

Pâdist "standing against," from pâd- "agaist, contrary to," → anti-, + ist present stem of istâdan "to stand" (Mid.Pers. êstâtan, O.Pers./Av. sta- "to stand; to set;" Av. hištaiti; cf. Skt. sthâ- "to stand;" Gk. histemi "put, place, weigh," stasis "a standing still;" L. stare "to stand;" Lith. statau "place;" Goth. standan; PIE base *sta- "to set, stand").
Pâdistân, from pâdist + -ân suffix of place and time.

1) The exercise of authority or power in a burdensome, cruel, or unjust manner.
2) An act or instance of oppressing or subjecting to cruel or unjust impositions or restraints.
3) The state of being oppressed (Dictionary.com).

M.E. oppressioun, from O.Fr. opresser "oppress; torment," from M.L. oppressare, from L. opprimere "press against, press down;" from op, variant of ob "against" + premere "to press, hold fast."

Setam, from Mid.Pers. sthmbk / stambag / "oppressive; obstinate," related to sitabr "strong, firm," staft "hard; firm, strong; fierce," Pers. seft "firm, hard, tight;" sitanbah "strong, robust, bold;" Av. aša.stəmbana- "having the support/firmness of aša;" Lith stembti "to oppose;" Gk. astemphes "unshakable."

An imperfection in the imaging properties of a lens or mirror. The main aberrations are → chromatic aberration, → spherical aberration, → coma, → astigmatism, → field curvature, → distortion.

→ optical; → aberration.

Any device such as a → lens, → prism, → mirror, and/or other similar objects used in an → optical system.

→ optical; → component.

A perception of visual stimuli in which what is perceived is in a way different from the way it is in reality. Same as visual illusion.

→ optical; → illusion.

The function that provides a full description of the imaging quality of an optical system. A combination of the → modulation transfer function (MTF) and the → phase transfer function (PTF) , the OTF describes the spatial (angular) variation as a function of spatial (angular) frequency.

→ optical; → transfer; → function.