Online Etymology Dictionary

oppressive (adj.): 1640s, from Medieval Latin oppressivus, from oppress-, past participle stem of opprimere (see oppress). Related: Oppressively; oppressiveness.
oppressor (n.): c.1400, from Old French opresseor, from Latin oppressor, from opprimere (see oppress (v.)).
opprobrious (adj.): "full of reproach, intended to bring disgrace," late 14c., from Old French oprobrieus (Modern French opprobrieux), or directly from Late Latin opprobriosus, from Latin opprobare "to reproach, taunt," from ob "against" (see ob-) + probrum "reproach, infamy." Etymological sense is "disgrace attached to conduct considered shameful." Related: Opprobriously; opprobriousness.
opprobrium (n.): 1680s, from Latin opprobrium "disgrace, infamy, scandal, dishonor," from opprobare (see opprobrious).
oppugn (v.): mid-15c., from Latin oppugnare "to fight against, attack, assail," from ob- "toward, against" (see ob-) + pugnare "to fight" (see pugnacious). Related: Oppugned; oppugning.
opry (n.): 1914, U.S. dialectal pronunciation of opera. Especially in Grand Ole Opry, a radio broadcast of country music from Nashville, registered as a proprietary name 1950.
opsimathy (n.): 1650s, from Greek opsimathia "learning late in life," from opse "late" (related to opiso "backward," opisthen "behind") + manthanein "to learn" (see mathematic). Related: Opsimath (n.).
opt (v.): 1877, from French opter "to choose" (16c.), from Latin optare "choose, desire" (see option). To opt out is attested from 1922. Related: Opted; opting.
optative: in reference to grammatical mood expressing wish or desire, 1520s, from Middle French optatif (15c.), from Late Latin optativus, from Latin optatus "wished, desired, longed for," past participle of optare "to choose, wish, desire" (see option).
optic (adj.): early 15c., from Middle French optique, obtique (c.1300) and directly from Medieval Latin opticus "of sight or seeing," from Greek 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 *okw- "to see" (see eye (n.)).
optical (adj.): 1560s, from optic + -al (1). Of abstract art, from 1964. Related: Optically.
optician (n.): 1680s, after French opticien "maker or seller of optical instruments;" see optic + -ian.
optics (n.): "science of sight and light," 1570s, from optic; also see -ics. Used for Medieval Latin optica (neuter plural), from Greek ta optika "optical matters," neuter plural of optikos "optic."
optimal (adj.): "most favorable," 1890, from Latin optimus (see optimum). Originally a word in biology. Related: Optimally.
optimism (n.): 1759 (in translations of Voltaire), from French optimisme (1737), from Modern Latin optimum, used by Gottfried Leibniz (in "Théodicée," 1710) to mean "the greatest good," from Latin optimus "the best" (see optimum). The doctrine holds that the actual world is the "best of all possible worlds," in which the creator accomplishes the most good at the cost of the least evil.
En termes de l'art, il l'appelle la raison du meilleur ou plus savamment encore, et Theologiquement autant que Géométriquement, le systême de l'Optimum, ou l'Optimisme. [Mémoires de Trévoux, Feb. 1737]
Launched out of philosophical jargon and into currency by Voltaire's satire on it in "Candide." General sense of "belief that good ultimately will prevail in the world" first attested 1841 in Emerson; meaning "tendency to take a hopeful view of things" first recorded 1819 in Shelley.
optimist (n.): 1759, from French optimiste (1752); see optimism + -ist.
optimistic (adj.): 1845, from optimist + -ic. Related: Optimistical (1809); optimistically.
optimization (n.): 1857, noun of action from optimize.
optimize (v.): 1844, "to act as an optimist," back-formation from optimist. Meaning "to make the most of" is first recorded 1857. Related: Optimized; optimizing.
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- "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- "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- (Germanic *ob-) "to work, produce in abundance," originally of agriculture later extended to religious acts (cf. 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 (e.g. 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-/*ous- "mouth" (cf. 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" (e.g. 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.
orange (n.): c.1300, 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.

Loss of initial n- probably due to confusion with definite article (e.g. 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. Not used as a color word until 1540s. 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" (cf. 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.
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).