Online Etymology Dictionary

optimum (n.): 1879, from Latin optimum, neuter singular of optimus "best" (used as a superlative of bonus "good"), probably related to ops "power, resources" (in which case the evolution is from "richest" to "the most esteemed," thus from PIE root *op- "to work") or to ob "in front of," with superlative suffix *-tumos. Originally in biology, in reference to "conditions most favorable" (for growth, etc.). As an adjective from 1885.
option (n.): c. 1600, "action of choosing," from French option (Old French opcion), from Latin optionem (nominative optio) "choice, free choice, liberty to choose," from root of optare "to desire, choose," from PIE root *op- (2) "to choose, prefer." Meaning "thing that may be chosen" is attested from 1885. Commercial transaction sense first recorded 1755 (the verb in this sense is from 1934). As a North American football play, it is recorded from 1954.
optional (adj.): 1765, from option + -al (1).
optometrist (n.): 1903; see optometry + -ist.
optometry (n.): 1886, from optometer (1738), an instrument for testing vision, from opto- "sight," from Greek optos "seen, visible" (see optic) + -metry. Probably influenced by French optométrie.
opulence (n.): c. 1510, from Middle French opulence (16c.), from Latin opulentia, from opulentus "wealthy," dissimilated from *op-en-ent-, related to ops "wealth, power, resources," opus "work, labor, exertion," from PIE root *op- (1) "to work, produce in abundance" (see opus).
opulent (adj.): c. 1600, from Middle French opulent, from Latin opulentem (nominative opulens) "wealthy, rich," from opulentus (see opulence).
opus (n.): "a work, composition," especially a musical one, 1809, from Latin opus "a work, labor, exertion" (source of Italian opera, French oeuvre, Spanish obra), from PIE root *op- (1) "to work, produce in abundance" (Germanic *ob-) "to work, produce in abundance," originally of agriculture later extended to religious acts (source also of Sanskrit apas- "work, religious act;" Avestan hvapah- "good deed;" Old High German uoben "to start work, to practice, to honor;" German üben "to exercise, practice;" Dutch oefenen, Old Norse æfa, Danish øve "to exercise, practice;" Old English æfnan "to perform, work, do," afol "power"). The plural, seldom used as such, is opera.
or (conj.): c. 1200, from Old English conjunction oþþe "either, or," related to Old Frisian ieftha, Middle Dutch ofte, Old Norse eða, Old High German odar, German oder, Gothic aiþþau "or." This was extended in early Middle English (and Old High German) with an -r ending, perhaps by analogy with "choice between alternative" words that ended thus (such as either, whether), then reduced to oþþr, at first in unstressed situations (commonly thus in Northern and Midlands English by 1300), and finally reduced to or, though other survived in this sense until 16c.

The contraction took place in the second term of an alternative, such as either ... or, a common construction in Old English, where both words originally were oþþe (see nor).
oracle (n.): late 14c., "a message from a god, expressed by divine inspiration," from Old French oracle "temple, house of prayer; oracle" (12c.) and directly from Latin oraculum "divine announcement, oracle; place where oracles are given," from orare "pray, plead" (see orator), with material instrumental suffix -culo-. In antiquity, "the agency or medium of a god," also "the place where such divine utterances were given." This sense is attested in English from c. 1400.
oracular (adj.): 1670s, from Latin oraculum (see oracle) + -ar.
oral (adj.): 1620s, from Late Latin oralis, from Latin os (genitive oris) "mouth, opening, face, entrance," from PIE *os- "mouth" (source also of Sanskrit asan "mouth," asyam "mouth, opening," Avestan ah-, Hittite aish, Middle Irish a "mouth," Old Norse oss "mouth of a river," Old English or "beginning, origin, front").

Psychological meaning "of the mouth as the focus of infantile sexual energy" (as in oral fixation) is from 1910. The sexual sense is first recorded 1948, in Kinsey. As a noun, "oral examination," attested from 1876. Related: Orally (c. 1600); orality. Os was the usual word for "mouth" in Latin, but as the vowel distinction was lost it became similar in sound to os "bone" (see osseous). Thus bucca, originally "cheek" but used colloquially as "mouth," became the usual word for "mouth" (see bouche).
orange (n.): c. 1300, of the fruit, from Old French orange, orenge (12c., Modern French orange), from Medieval Latin pomum de orenge, from Italian arancia, originally narancia (Venetian naranza), alteration of Arabic naranj, from Persian narang, from Sanskrit naranga-s "orange tree," of uncertain origin. Not used as a color word until 1540s.

Loss of initial n- probably due to confusion with definite article (as in une narange, una narancia), but perhaps influenced by French or "gold." The name of the town of Orange in France (see Orangemen) perhaps was deformed by the name of the fruit. Orange juice is attested from 1723.

The tree's original range probably was northern India. The Persian orange, grown widely in southern Europe after its introduction in Italy 11c., was bitter; sweet oranges were brought to Europe 15c. from India by Portuguese traders and quickly displaced the bitter variety, but only Modern Greek still seems to distinguish the bitter (nerantzi) from the sweet (portokali "Portuguese") orange. Portuguese, Spanish, Arab, and Dutch sailors planted citrus trees along trade routes to prevent scurvy. On his second voyage in 1493, Christopher Columbus brought the seeds of oranges, lemons and citrons to Haiti and the Caribbean. Introduced in Florida (along with lemons) in 1513 by Spanish explorer Juan Ponce de Leon. Introduced to Hawaii 1792.
orangeade (n.): from French, from orange + ending from lemonade.
Orangemen (n.): secret society founded 1795 in Belfast to promote Protestant power in Northern Ireland, named for William of Orange (who became King William III of England and triumphed in Ireland at the head of a Protestant army at the Battle of the Boyne), of the German House of Nassau. His cousins and their descendants constitute the royal line of Holland.

The name is from the town of Orange on the Rhone in France, which became part of the Nassau principality in 1530. Its Roman name was Arausio, which is said in 19c. sources to be from aura "a breeze" and a reference to the north winds which rush down the valley, but perhaps this is folk etymology of a Celtic word. The name subsequently was corrupted to Auranche, then Orange. The town has no obvious association with the fruit other than being on the road from Marseilles to Paris, along which masses of oranges were transported to northern France and beyond. In this roundabout way the political/religious movement of Northern Irish Protestantism acquired an association with the color orange, the Irish national flag acquired its orange band, and Syracuse University in New York state acquired its "Otto the Orange" mascot.
orangutan (n.): 1690s, from Dutch orang-outang (1631), from Malay orang utan, literally "man of the woods," from orang "man" + utan, hutan "forest, wild." It is possible that the word originally was used by town-dwellers on Java to describe savage forest tribes of the Sunda Islands and that Europeans misunderstood it to mean the ape. The name is not now applied in Malay to the animal, but there is evidence that it was used so in 17c. [OED]
orate (v.): c. 1600, "to pray, to plead," from Latin oratus, past participle of orare "speak, pray, plead, speak before a court or assembly" (see orator). The meaning "make a formal speech" emerged c. 1860 in American English as a back-formation of oration. Related: Orated; orating.
oration (n.): late 14c., "prayer," from Late Latin orationem (nominative oratio) "a speaking, speech, discourse; language, faculty of speech, mode of expressing; prayer," noun of action from past participle stem of Latin orare "to pray, plead, speak before an assembly" (see orator). Meaning "formal speech, discourse" first recorded c. 1500.
orator (n.): late 14c., "one who pleads or argues for a cause," from Anglo-French oratour (Modern French orateur), from Latin orator "speaker," from orare "to speak, speak before a court or assembly, pray, plead," from PIE root *or- "to pronounce a ritual formula" (source also of Sanskrit aryanti "they praise," Homeric Greek are, Attic ara "prayer," Hittite ariya- "to ask the oracle," aruwai- "to revere, worship"). Meaning "public speaker" is attested from early 15c.
oratorical (adj.): 1580s, from orator or oratory + -ical, or else from Latin oratorius (see oratory (n.1)). Related: Oratorical; oratorically.
oratorio (n.): "long musical composition, usually with a text based on Scripture," 1727 (in English from 1640s in native form oratory), from Italian oratorio (late 16c.), from Church Latin oratorium (see oratory (n.2)), in reference to musical services in the church of the Oratory of St. Philip Neri in Rome, where old mystery plays were adapted to religious services.
oratory (n.1): "formal public speaking, the art of eloquence," 1580s, from Latin (ars) oratoria "oratorical (art)," fem. of oratorius "of speaking or pleading, pertaining to an orator," from orare "to speak, pray, plead" (see orator).
oratory (n.2): "small chapel," c. 1300, from Old French oratorie and directly from Late Latin oratorium "place of prayer" (especially the Oratory of St. Philip Neri in Rome, where musical services were presented), noun use of an adjective, as in oratorium templum, from neuter of Latin oratorius "of or for praying," from orare "to pray, plead, speak" (see orator).
orb (n.): mid-15c., "sphere, globe, something spherical or circular," from Old French orbe "orb, globe" (13c.) and directly from Latin orbem (nominative orbis) "circle, disk, ring, hoop, orbit," probably related to orbita "wheel track, rut," of unknown origin. Watkins suggests a connection with the root of orchid.

A three-dimensional extension of a word originally describing two-dimensional shapes. Astronomical sense is in reference to the hollow spheres that carried the planets and stars in the Ptolemaic system. As a verb from c. 1600. Orb weaver spider is first recorded 1889.
orbicular (adj.): "round, circular, spherical," mid-15c., from Old French orbiculaire "round, circular," or directly from Late Latin orbicularis "circular, orbicular," from Latin orbiculus, diminutive of orbis "circle" (see orb). Related: Orbicularity.
orbit (n.): late 14c., "the eye socket," from Old French orbite or directly from Medieval Latin orbita, transferred use of Latin orbita "wheel track, beaten path, rut, course, orbit" (see orb). Astronomical sense first recorded 1690s in English; it was in classical Latin, revived in Gerard of Cremona's translation of Avicenna. The Old English word for "eye socket" was eaghring.
orbit (v.): 1946, from orbit (n.). Related: Orbited; orbiting.
orbital (adj.): 1540s, with reference to eye sockets; 1839 with reference to heavenly bodies; from orbit (n.) + -al (1).
orbiter 1954: agent noun from orbit (v.).
orc (n.): "ogre, devouring monster," Old English orcþyrs, orcneas (plural), perhaps from a Romanic source akin to ogre, and ultimately from Latin Orcus "Hell," a word of unknown origin. Revived by J.R.R. Tolkien (1892-1973) as the name of a brutal race in Middle Earth.
But Orcs and Trolls spoke as they would, without love of words or things; and their language was actually more degraded and filthy than I have shown it. ["Return of the King," 1955]
orca (n.): "killer whale," introduced as a generic term for the species by 1841, from earlier use in scientific names, from Latin orca "cetacean, a kind of whale." Earlier in English, orc, ork "large whale" (c. 1590), from French orque, had been used vaguely of sea monsters (see orc).
orchard (n.): late Old English orceard "fruit garden," earlier ortgeard, perhaps reduced from wortgeard, from wort (Old English wyrt "vegetable, plant root") + geard "garden, yard" (the word also meant "vegetable garden" until 15c.); see yard (n.1). First element influenced in Middle English by Latin hortus (in Late Latin ortus) "garden," which also is from the root of yard (n.1).
orchestra (n.): c. 1600, "area in an ancient theater for the chorus," from Latin orchestra, from Greek orkhestra, semicircular space where the chorus of dancers performed, with suffix -tra denoting place + orkheisthai "to dance," intensive of erkhesthai "to go, come," from PIE root *ergh- "to mount" (source also of Sanskrit rghayati "trembles, rages, raves," rnoti "rises, moves," arnah "welling stream;" Old Persian rasatiy "he comes;" Greek ornynai "to rouse, start;" Latin oriri "to rise," origo "a beginning;" Gothic rinnan, Old English irnan "to flow, run"). In ancient Rome, it referred to the place in the theater reserved for senators and other dignitaries. Meaning "group of musicians performing at a concert, opera, etc." first recorded 1720; "part of theater in front of the stage" is from 1768.
orchestral (adj.): 1811, from orchestra + -al (1).
orchestrate (v.): "to compose or arrange (music) for an orchestra," 1855, back-formation from orchestration. The figurative sense is attested from 1883. Related: Orchestrated; orchestrating.
orchestration (n.): 1840, from French orchestration or else a native noun of action from orchestrate.
orchid (n.): 1845, introduced by John Lindley in "School Botanty," from Modern Latin Orchideæ (Linnaeus), the plant's family name, from Latin orchis, a kind of orchid, from Greek orkhis (genitive orkheos) "orchid," literally "testicle," from PIE *orghi-, the standard root for "testicle" (source also of Avestan erezi "testicles," Armenian orjik, Middle Irish uirgge, Irish uirge "testicle," Lithuanian erzilas "stallion"). The plant so called because of the shape of its root. Earlier in English in Latin form, orchis (1560s), and in Middle English it was ballockwort (c. 1300; see ballocks). Marred by extraneous -d- in an attempt to extract the Latin stem.
ordain (v.): late 13c., "to appoint or admit to the ministry of the Church," from stem of Old French ordener "place in order, arrange, prepare; consecrate, designate" (Modern French ordonner) and directly from Latin ordinare "put in order, arrange, dispose, appoint," from ordo (genitive ordinis) "order" (see order (n.)). The notion is "to confer holy orders upon." Meaning "to decree, enact" is from c. 1300; sense of "to set (something) that will continue in a certain order" is from early 14c. Related: Ordained; ordaining.
ordeal (n.): Old English ordel, ordal, "trial by physical test," literally "judgment, verdict," from Proto-Germanic noun *uz-dailjam (source also of Old Saxon urdeli, Old Frisian urdel, Dutch oordeel, German urteil "judgment"), literally "that which is dealt out" (by the gods), from *uzdailijan "share out," related to Old English adælan "to deal out" (see deal (n.1)). Curiously absent in Middle English, and perhaps reborrowed 16c. from Medieval Latin or Middle French, which got it from Germanic.

The notion is of the kind of arduous physical test (such as walking blindfolded and barefoot between red-hot plowshares) that was believed to determine a person's guilt or innocence by immediate judgment of the deity, an ancient Teutonic mode of trial. English retains a more exact sense of the word; its cognates in German, etc., have been generalized.

Metaphoric extension to "anything which tests character or endurance" is attested from 1650s. The prefix or- survives in English only in this word, but was common in Old English and other Germanic languages (Gothic ur-, Old Norse or-, etc.) and originally was an adverb and preposition meaning "out."
order (n.): early 13c., "body of persons living under a religious discipline," from Old French ordre "position, estate; rule, regulation; religious order" (11c.), from earlier ordene, from Latin ordinem (nominative ordo) "row, rank, series, arrangement," originally "a row of threads in a loom," from Italic root *ord- "to arrange, arrangement" (source of ordiri "to begin to weave;" compare primordial), of unknown origin.

Meaning "a rank in the (secular) community" is first recorded c. 1300; meaning "command, directive" is first recorded 1540s, from the notion of "to keep in order." Military and honorary orders grew our of the fraternities of Crusader knights. Business and commerce sense is attested from 1837. In natural history, as a classification of living things, it is first recorded 1760. Meaning "condition of a community which is under the rule of law" is from late 15c.

Phrase in order to (1650s) preserves etymological notion of "sequence." The word reflects a medieval notion: "a system of parts subject to certain uniform, established ranks or proportions," and was used of everything from architecture to angels. Old English expressed many of the same ideas with endebyrdnes. In short order "without delay" is from 1834, American English; order of battle is from 1769.
order (v.): c. 1200, "give order to, to arrange in order," from order (n.). Meaning "to give orders for or to" is from 1540s. Related: Ordered; ordering.
orderly (adv.): late 15c., "in due order," from order + -ly (2).
orderly (n.): "military attendant who carries orders," 1781, short for orderly corporal, etc. Extended 1809 to an attendant at a hospital (originally a military hospital) charged with keeping things in order and clean. See orderly (adj.).
orderly (adj.): "arranged in order," 1570s, from order (n.) + -ly (1).
ordinal (n.): early 14c., "book setting forth the order of services in the Church," from Late Latin adjective ordinalis (see ordinal (adj.)).
ordinal (adj.): late 14c., "regular, ordinary," from Old French ordinel and directly from Late Latin ordinalis ""showing order, denoting an order of succession," from Latin ordo (genitive ordinis) "row, series" (see order (n.)). Meaning "marking position in an order or series" is from 1590s.
ordinance (n.): c. 1300, "an authoritative direction, decree, or command" (narrower or more transitory than a law), from Old French ordenance (Modern French ordonnance) or directly from Medieval Latin ordinantia, from Latin ordinantem (nominative ordinans), present participle of ordinare "put in order" (see ordain). By early 14c. senses had emerged of "arrangement in ranks or rows" (especially in order of battle), also "warlike provisions, equipment" (a sense now in ordnance).
ordinary (adj.): early 15c., "belonging to the usual order or course," from Old French ordinarie "ordinary, usual" and directly from Latin ordinarius "customary, regular, usual, orderly," from ordo (genitive ordinis) "order" (see order (n.)). Its various noun usages, dating to late 14c. and common until 19c., now largely extinct except in out of the ordinary (1893). In British education, Ordinary level (abbrev. O level), "lowest of the three levels of General Certificate of Education," is attested from 1947. Related: Ordinarily.
ordinate (adj.): late 14c., from Latin ordinatus, past participle of ordinare "arrange, set in order" (see ordain). Related: Ordinately.
ordinate (v.): 1560s, from Latin ordinatus, past participle of ordinare "arrange, set in order" (see ordain). Related: Ordinated; ordinating.