An Etymological Dictionary of Astronomy and Astrophysics

1. General: The state or quality of being opaque.
   

2. A measure of the absorption of photons on their way from the stellar center to the surface. Opacity depends upon the frequency of the radiation, the density, the chemical composition, and the thermodynamic state of the gas. For a given density, the hotter the gas the lower the opacity, since the gas absorbs less readily, as described by → Kramers’ law.
   Conversely, the cooler the gas the higher the opacity. See also → stellar pulsation, → kappa mechanism, → valve mechanism, → partial ionization zone.

Etymology (EN): From Fr. opacité, from L. opacitatem (nom. opacitas) “shade, shadiness,” from opacus “shaded, dark, opaque.”

Etymology (PE): Kederi, from keder “opaque,” from Ar. kader + -i suffix forming nouns from adjectives.

A → mineral, an amorphous form of → silica, SiO₂ with some → water of → hydration,
found in many varieties and colors, including a form that is milky white.

Etymology (EN): M.E., from M.Fr. opalle, from L. opalus, from Gk. opallios “opal, gem;” probably from a source akin to Skt. upala “jewel, precious stone.”

Etymology (PE): Loan from E., as above.

1. The state of being → opalescent, or emitting an → iridescence like that of an opal.
   

2. Physics: The milky → iridescent appearance of a dense transparent medium when it is illuminated by → polychromatic visible radiation (such as sunlight) due to local → fluctuations in its density and therefore in its → refractive index. → critical opalescence.

See also: → opal; → -escence.

Exhibiting a play of colors like that of the opal.

See also: → opal; → -escent.

General: Not permitting a radiation to pass through.
Meteo.: A condition where a material, such as a cloud, blocks the passage of radiant energy, especially light.

See also: Adj. form of → opacity.

Not closed.
Math.: → open interval; → open set.

Etymology (EN): O.E. open “not closed down, raised up,” also “uncovered, bare; plain, evident,” related to up; from P.Gmc. *upana (cf. O.N. opinn, Swed. öppen, Dan. aaben, O.Fris. epen, O.H.G. offan “open”), from PIE *upo “up from under, over;” cf. L. sub; Gk. hypo; O.Pers. upā (prep.) “under, with;” Av. upā, upa (prep.; prevb) “toward, with, on, in;”
Mod.Pers. bâ “with,” from abâ;
Skt. úpa (adv., prevb., prep.) “toward, with, under, on.”

Etymology (PE): Bâz “open,” from Mid.Pers. abâz-, apâc-, O.Pers. apa- [pref.] “away, from;” Av. apa- [pref.] “away, from,”
apaš [adv.] “toward the back;” cf. Skt. ápāñc “situated behind.”

A loose grouping of dozens or hundreds of young stars distributed in a region a few light-years across. Open clusters are relatively young, typically containing many hot, highly luminous stars. They are located within the disk of the Galaxy, whence their older name Galactic clusters.

See also: → open; → cluster.

An interval that does not include its two endpoints.

See also: → open; → interval.

In the context of solar physics, a → magnetic field line when it crosses the solar surface only once, i.e., when it goes from surface to infinity. This is the case at a sufficiently large scale in → coronal holes. This is mostly not the case in → active regions.

See also: → open; → magnetic; → field; → line.

A → set consisting of points having → neighborhoods wholly contained in the set, as the set of points within a circle.

See also: → open; → set.

A space of infinite volume without any boundary. Triangles which lie on the surface of an open space will have a sum of angles which is less than 180°. An open space has a negative → curvature. See also → open Universe, → closed space.

See also: → open; → space.

Thermodynamics: A system which can exchange both energy and matter with the surroundings. → closed system; → isolated system.

See also: → open; → system.

A → Freidmann-Lemaitre  → cosmological model in which → space is → infinite and of → negative 
→ curvature or → Euclidean, and which expands forever.

See also: → open; → universe.

In → predicate logic, a → well-formed formula with one or more → free occurrences of → variables.

See also: → open; → wff.

The capability of being put into use, operation, or practice.

See also: → operable; → -ity.

Capable of operating or of being operated.

See also: → operate; → -able.

To function or work; to make something function or work.

Etymology (EN): From L. operari “to work, labor,” L. opus “a work, labor, exertion,” Av. *āpah-, *apah- “to do, operate,” see below, Skt.
ápas- “work, action, religious act;”
O.H.G. uoben “to start work, to practice, to honor;” Ger. üben “to exercise, practice;” Du. oefenen; O.E. æfnan “to perform, work, do,” afol “power”); PIE base *op- “to work, perform.”

Etymology (PE): Âpâridan, from âpâr-, from Av. *āp(ah)- “to do, operate,” as above, + suffix -ar (as in vadar- “weapon,” zafar- “jaw,” baēvar- “thousand,” and so on), shifted to -âr, + -idan suffix of infinitives. The Av. *āpah- “to do, operate,” is extant in Mod.Pers. xub “good;” Mid.Pers. hwp, xub “good;” from Av. huuāpah- “doing good work, masterly,” from huu-, hv- “good” → eu- + āpah- “work, deed,” hauuapanha- “creativity;” cf. Skt. sv-ápas- “doing good work, skillful;” PIE base *op-, as above.

The program that, after being initially loaded into the → computer by a boot program, → manages all the other → programs in a computer.

See also: → operating; → system.

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.

See also: Verbal noun of → operate

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

See also: 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.

See also: → 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.

See also: → operation; → -ism.

Math.: Something that acts on another function to produce another function. In linear algebra an “operator” is a linear operator. In calculus an “operator” may be a differential operator, to perform ordinary differentiation, or an integral operator, to perform ordinary integration.

See also: From → operate; + → -or.

A small satellite of → Uranus, the second nearest to the planet, discovered from the images taken by the Voyager 2 spacecraft in 1986. Also denoted Uranus II, it has a diameter of 32 km. Ophelia is one of the two → shepherd moons that keep the planet’s Epsilon ring, the other being → Cordelia.

See also: Ophelia is the daughter of Polonius in Shakespeare’s Hamlet.

The Serpent Holder. An extensive constellation located in the equatorial regions of the sky at about 17h 20m right ascension, 5° south declination. Although this constellation is not part of the zodiac, the Sun passes through it in December each year. Ophiuchus contains five stars of second magnitude and seven of third magnitude. Other designations: Serpent Bearer, Serpentarius.
Abbreviation: Oph, genitive: Ophiuchi.

Etymology (EN): L. Ophiuchus, from Gk. ophioukhos “holding a serpent,” from ophis “serpent” + echein “to hold, have, keep.” The most recent interpretation is that the figure represents the great healer
Asclepius, a son of the god Apollo, who learned the secrets of keeping death at bay after observing one serpent bringing another healing herbs. To prevent the entire human race from becoming immortal under Asclepius’ care, Zeus killed him with a bolt of lightning, but later placed his image in the heavens to honor his good works.

Etymology (PE): Mâr-afsâ “a tamer or charmer of serpents; one who cures the snake-bitten by incantation,” from mâr “snake, serpent” (Mid.Pers. mâr “snake;” Av. mairya- “snake, serpent”) + afsâ agent noun of afsâyidan, from afsun “incantation” (Mid.Pers. afsôn “spell, incantation,” afsûdan, afsây- “to enchant, protect by spell”).

To hold or express an opinion.

See also: Verb for → opinion.

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).

Etymology (EN): M.E., from O.Fr., from L. opinion- “opinion, conjecture; appreciation,” from opinari “to think, judge, suppose,” from PIE *op- “to choose.”

Etymology (PE): 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.

The upper bound to the mass of a → neutron star, the mass beyond which the pressure of neutron → degenerate matter is not capable of preventing the → gravitational collapse which will lead to the formation of a → black hole. Modern estimates range from approximately 1.5 to 3.0 → solar masses. The uncertainty in the value reflects the fact that the → equation of state for → overdense matter is not well-known.

See also: Oppenheimer, J.R., Volkoff, G.M., 1939, Physical Review 55, 374. Named after Robert Oppenheimer (1904-1967), an American theoretical physicist, and
George Volkoff (1914-2000), a Canadian physicist, who first calculated this limit.
Oppenheimer is widely known for his role as the scientific director of the Manhattan Project,
the World War II effort to develop the first nuclear weapons at the secret
Los Alamos laboratory in New Mexico; → limit.

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

Etymology (EN): 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.

Etymology (PE): Pâdistgar, from pâdist, → opposition, + -gar, → -or.

1. Appropriate, favorable, or suitable.
   

2. Occurring or coming at an appropriate time; well-timed (Dictionary.com).

Etymology (EN): M.E., from O.Fr. opportun and directly from L. opportunus “fit, convenient, suitable,” from the phrase ob portum veniens
“coming toward a port,” literally “a wind blowing to harbor,” from ob “to, toward” + portus “access, harbor.”

Etymology (PE): Nikvâ “appropriate, suitable,” from nik, nêk, neku “good, beautiful, elegant;” Mid.Pers. nêk, nêvak, nêkôg “good, beautiful;” O.Pers. naiba-

• -vâ relation suffix (as in pišvâ, pilévâ); alternatively, nikvâ “good/appropriate wind,” from nik + vâ “wind,” variant of bâd, → wind, in several dialects.

The policy or practice, as in politics, business, or one’s personal affairs, of adapting actions, decisions, etc., to expediency or effectiveness regardless of the sacrifice of ethical principles (Dictionary.com).

See also: → opportune + → -ism.

A person who adapts his actions, responses, etc, to take advantage of opportunities, circumstances, etc. (Dictionary.com).

See also: → opportune + → -ist.

1. An appropriate or favorable time or → occasion.
   

2. A situation or condition favorable for attainment of a goal (Dictionary.com).

See also: → opportune + → -ity.

1. To act against or provide resistance to.
   

2. To stand in the way of; hinder; obstruct (Dictionary.com).

Etymology (EN): M.E., from O.Fr. oposer “to oppose, resist; contradict,” from poser “to place, lay down,” blended with L. opponere “to oppose, to object,” → position.

Etymology (PE): Pâdistidan, infinitive from pâdist, → opposition.

1. Situated, placed, or lying face to face with something else or each other, or in corresponding positions with relation to an intervening line, space, or thing: opposite ends of a room (Dictionary.com).
   

2. Contrary or radically different in some respect common to both, as in nature, qualities, direction, result, or significance; opposed (Dictionary.com).
   

3. An → antonym.

Etymology (EN): M.E., from M.Fr., from L. oppositus, p.p. of opponere,
→ opposition.

Etymology (PE): 1) Ru-be-ru “face to face,” → surface.

2. Pârun, short for pâdrun, from pâd-, → counter, + -run “side, direction” (as in birun, darun, vârun), → out.
   

3. Pâdcem, → antonym.

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.

Etymology (EN): Verbal noun of → oppose.

Etymology (PE): 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.

To burden with cruel or unjust impositions or restraints; subject to a burdensome or harsh exercise of authority or power (Dictionary.com).

Etymology (EN): M.E. oppressen, from O.Fr. opresser “oppress, torment, smother,” from M.L. oppressare, from L. opprimere “press against, press together, press down; subdue, prosecute relentlessly,” from op variant of ob “against” + premere “to press, hold fast.”

Etymology (PE): Infinitive from setam, → oppression.

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).

Etymology (EN): 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.”

Etymology (PE): 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.”

To make a choice; choose (usually followed by for).

Etymology (EN): From Fr. opter “to choose,” from L. optare “to choose, desire, wish for,” from L. optare “to desire, choose,” from PIE root *op- “to choose, prefer.”

Etymology (PE): Optidan, from L. optare, as above.

Of, relating to, or constituting a verbal mood that is expressive of wish or desire.

Etymology (EN): From M.Fr. optatif, from L. optativus, from optatus, p.p. of optare, → opt, + -ivus, → -ive.

Etymology (PE): Optâné, optmand, from opt present stem of optidan, → opt, + adj. suffixes -âné, -mand. -yi.

1. Of or pertaining to the eye or sight.
   
2. Same as → optical.

Etymology (EN): From M.Fr. optique, from M.L. opticus “of sight or seeing,” from Gk. optikos “of or having to do with sight,” from optos “seen, visible,” from op-, root of opsesthai “be going to see,” related to ops “eye,” from PIE *ok^w- “eye/see.”

Etymology (PE): 1) Nuri, nurik, from nur, → light + -i, -ik adj. suffix → -ic.
2) Didgâni, related to didgân “eyes,” plural of didé “eye; seen,” from didan “to see” (Mid.Pers. ditan “to see, regard, catch sight of, contemplate, experience;” O.Pers. dī- “to see;” Av. dā(y)- “to see,” didāti “sees;” cf.
Skt. dhī- “to perceive, think, ponder; thought, reflection, meditation,” dādhye; Gk. dedorka “have seen”).

The direction in a doubly refracting crystal in which light is propagated without double refraction.

See also: → optic; → axis.

1. Of, pertaining to, or applying optics or the principles of optics.
   
2. Of or pertaining to sight or vision; visual; of or pertaining to the eye.

Etymology (EN): From → optic + → -al.

Etymology (PE): → optic.

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

See also: → optical; → aberration.

The property possessed by some substances and their solutions of rotating the plane of vibration of → polarized light. When a beam of → linearly polarized light is sent through an optically active substance, such as crystalline quartz and sugar solution, the direction of vibration of the emerging linearly polarized light is found to be different from the original direction. Those which rotate the → plane of polarization to the right, for an observer looking in the incoming beam, are called → dextrorotatory or right handed; those which rotate it to the left, → levorotatory or left handed. Optical activity may be due to an asymmetry of molecules of a substance (solutions of cane sugar) or it may be a property of a crystal as a whole (crystalline quartz).

See also: → optical; → activity.

The mathematical evaluation of an optical system to determine its basic optical properties and image quality characteristics.

See also: → optical; → analysis.

An instrument used to test lenses by utilizing the → optical transfer function. It consists of a HeNe laser, a beamsplitter and two mirrors.

See also: → optical; → autocorrelator.

Line passing through the optical center and the center of curvature of a → spherical mirror or → lens. Same as → principal axis.

See also: → optical; → axis.

A track or table on which sources, lenses, mirrors, and other optical components can be mounted and moved. It is used in optics experiments.

Etymology (EN): → optical; bench, M.E., from O.E. benc “long seat;” cf. Da. bænk, M.Du. banc, O.H.G. banch.

Etymology (PE): Miz “table,” originally “preparations for entertaining a guest; guest;” Mid.Pers. mêzd “offering, meal;” nurik, nuršenâxti, → optical.

Of a thin lens, a point situated at the geometrical center of the lens, through which an incident ray passes without being deviated.

See also: → optical; → center.

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

See also: → optical; → component.

An astronomical object with usually weak emission in the → visible found to be the optical representation of the object radiating chiefly in other
→ wavelengths of the → electromagnetic spectrum.

See also: → optical; → counterpart.

The transmittance of a point on a photographic negative equal to the log to the base 10 of the reciprocal of the transmittance through the negative at that point.

See also: → optical; → density.

1. A measure of how much radiation is absorbed when traveling through a medium (such as the atmosphere of a star or the interstellar medium) from the source to a given point. It depends on the type of medium and the frequency of radiation. It is defined as a dimensionless quantity dτ_λ = κ_λ ρ dx, where κ_λ is the extinction coefficient, ρ the density, and dx the path length.
   

2. The ratio of the intensity of radiation (light or radio waves) incident on a ring to that emerging from the opposite face of the ring, expressed as a natural logarithm. If the reduction in intensity is by a factors of e (= 2.718), the ring is said to have an optical depth of 1. Normal (or normalized) optical depth is optical depth corrected for oblique (non-vertical) viewing. In ring studies, the terms optical depth and optical thickness are generally used interchangeably. These terms generally refer to a particular wavelength (Ellis et al., 2007, Planetary Ring Systems, Springer).

See also: → optical; → depth.

A pair of stars that lie close to each other in the sky by chance, but are not physically associated, in contrast to a true → binary star.

See also: → optical; → double star.

A thin filament of drawn or extruded glass or plastic having a central core and a cladding of lower index material to promote internal reflection. It may be used singly to transmit pulsed optical signals (communications fiber) or in bundles to transmit light or images.

See also: → optical; → fiber.

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.

See also: → optical; → illusion.

An instrument that either processes light waves to enhance an image or analyzes light waves to determine one of a number of characteristic properties.

See also: → optical; → instrument.

An → astrophysical jet which is visible in the optical range of the electromagnetic radiation.

See also: → optical; → jet.

(polar flattening) The ratio of the difference between equatorial and polar diameters to the equatorial diameter. A sphere has an oblateness of 0; an infinitely thin disk has an oblateness of 1 (Ellis et al., 2007, Planetary Ring Systems, Springer).

See also: → optical; → oblateness.

In → geometric optics, the distance a light ray would travel in a vacuum in the same time it travels from one point to another, a specified distance, through one or more optical media.

See also: → optical; → path.

A member of a rare class of pulsars, such as the → Crab pulsar and → Vela pulsar, which can be detected in the visible spectrum.

See also: → optical; → pulsar.

A process in which light energy is used to raise electrons from a lower energy level in an atom or molecule to a higher one. It is commonly used in laser construction, to pump the active laser medium so as to achieve population inversion. The technique was developed by 1966 Nobel Prize winner Alfred Kastler in the early 1950’s.

See also: → optical; → pumping.

A collection of lens, prisms, mirrors, and/or other devices, placed in some specified configuration, to act on light (reflect, refract, disperse, polarize, etc.) and perform some definite optical function.

See also: → optical; → system.

Same as → optical depth.

See also: → optical; → thickness.

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.

See also: → optical; → transfer; → function.

The optical portion of the electromagnetic spectrum that passes through the atmosphere all the way to the ground.

See also: → optical; → window.

Adverb of → optical.

Etymology (EN): → optical + -ly.

Etymology (PE): Nurâné, from nur, → light, + -âné “-ly;” nurikâné, from nurik, → optical, + -âné “-ly.”

Relating to → optical activity.

See also: → optically; → active.

The qualifier of a medium in which the → optical depth is large,
significantly larger than 1.

See also: → optically; → thick.

A wind with the → sonic point located at large optical depth for continuum. In particular, → Wolf-Rayet star winds are → optically thick. However, the outer parts of W-R winds are → optically thin for continuum, and in those regions the matter flow is driven by the same mechanism as in the winds of OB stars.

See also: → optically; → thick; → wind.

The qualifier of a medium in which the → optical depth is large,
significantly smaller than 1.

See also: → optically; → thin.

A member of a small subset of quasars consisting of bright radio galaxies whose flux of visible light output can vary by as much as 50% in a single day.

See also: → optically; → violent; → variable; → quasar.

1. A maker or seller of optical glass.
   
2. A person specialized in optical instruments.

Etymology (EN): From Fr. opticien, from M.L. optic(a), → optics, + -ien “-ian.”

Etymology (PE): 1) Eynak-sâz “eyeglass maker,” from eynak→ eyeglasses + sâz agent noun of sâxtan, sâzidan “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. Nurikâr, nurik-kâr “optics performer, optics workman, optics specialist,” from nurik, → optics, + -kâr
   variants -gar,-gâr,
   from kar-, kardan “to do, to make” (Mid.Pers. kardan, O.Pers./Av. kar- “to do, make, build,” Av. kərənaoiti “makes,” cf. Skt. kr- “to do, to make,” krnoti “makes,” karma “act, deed;” PIE base k^wer- “to do, to make”).

The branch of physics that deals with the properties and phenomena of electromagnetic radiation in the wavelength range extending from the ultraviolet (at about 40 nm) to the far-infrared (at 1 mm) and with vision.

Etymology (EN): Optics, from optic, from M.Fr. optique, from M.L. opticus “of sight or seeing,” from Gk. optikos “of or having to do with sight,” from optos “seen, visible,” from op-, root of opsesthai “be going to see,” related to ops “eye,” from PIE *ok^w- “eye; to see” (→ eye); → -ics.

Etymology (PE): Nurik, from nur, → light, + -ik→ -ics. Nuršenâsi, from nur, → light, + šenâsi→ -logy.

One that minimizes or maximizes some quantity or combination of quantities,
such as time, energy, distance, path, etc.

See also: Optimal, adj. of → optimum.

General: The fact of optimizing. The condition of being optimized.
→ optimize.
Computer science: Improving a system to reduce runtime, bandwidth, memory requirements, or other property of a system.

See also: Verbal noun of → optimize

General: To make as effective, perfect, or useful as possible.
Math.:

To determine the maximum or minimum values of a specified function by systematically choosing the values of the variables from within an allowed set.

Etymology (EN): From opti(mum), → optimum, + → -ize.

Etymology (PE): Behinidan, from behin, → optimum, + -idan infinitive suffix. Behin sâxtan compound verb from behin + sâxtan, sâzidan “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”).

In computer science, a program that optimizes the speed or resource utilization. → optimize.

See also: Agent noun of → optimize.

The best or most favorable point, degree, amount, etc. The greatest degree or best result obtained or obtainable under specific conditions.

Etymology (EN): From L. optimum, neuter singular of optimus “best” (used as a suppletive superlative of bonus “good”).

Etymology (PE): Behiné, from behin superlative of beh “good, fine” (Mid.Pers. veh “better, good;” O.Pers. vahav-, vahu-; Av. vah-, vohu- “good;” cf. Skt. vasu- “good;” Hittite wasu-; Gaulish vesus “good”) + -in superlative suffix + -é nuance suffix.

1. The power or right of choosing.
   

2. Something that may be or is chosen; choice.
   

3. The act of choosing (Dictionary.com).

See also: → opt; → -tion.

Left to one’s choice; not required or mandatory (Dictionary.com).

See also: → option; → -al.

Any of various instruments for measuring refractive errors of the eye.

Etymology (EN): From opto- “vision; eye; optis,” combining form from Gk. optos “seen, visible,” from opsesthai “be going to see,” related to ops “eye;” → -meter.

Etymology (PE): Did, → vision; -sanj, → -meter.