Online Etymology Dictionary

oriole (n.): 1776, from French oriol "golden oriole," Old Provençal auriol, from Medieval Latin oryolus, from Latin aureolus "golden," from PIE *aus- (2) "gold" (see aureate). Originally in reference to the golden oriole (Oriolus galbula), a bird of black and yellow plumage that summers in Europe (but is uncommon in England). Applied from 1791 to the unrelated but similarly colored North American species Icterus baltimore.
Orion: bright constellation, late 14c., from Greek Oarion, name of a giant in Greek mythology, loved by Aurora, slain by Artemis, of unknown origin, though some speculate on Akkadian Uru-anna "the Light of Heaven." Another Greek name for the constellation was Kandaon, a title of Ares, god of war, and the star pattern is represented in many cultures as a giant (such as Old Irish Caomai "the Armed King," Old Norse Orwandil, Old Saxon Ebuðrung).
orison (n.): late 12c., from Anglo-French oreison, Old French oreisun (12c., Modern French oraison) "oration," from Latin orationem (nominative oratio) "speech, oration," in Church Latin "prayer, appeal to God," noun of action from orare (see orator). Etymologically, a doublet of oration.
Orkney: name of a group of islands off the north coast of Scotland, from Old Norse Orkney-jar "Seal Islands," from orkn "seal," probably imitative of its bark. Related: Orkneyman.
Orlando: masc. proper name, Italian form of Roland (q.v.). The city in Florida, U.S., so called from 1857, supposedly in honor of a U.S. soldier, Orlando Reeves, who was killed there in 1835 by Seminoles. It had been settled c. 1844 as Jernigan.
Orleans: city in France, French Orléans, Roman Aurelianum, named 3c. C.E. in honor of emperor Aurelius (having formerly been called Genabum, from roots *gen- "bend" (in a river) + *apa "water").
Orlon: proprietary name (Du Pont) of synthetic textile fiber, 1948, an invented word (compare nylon).
ormolu (n.): "alloy of copper, zinc, and tin, resembling gold," 1765, from French or moulu, literally "ground gold," from or "gold" (from Latin aurum, from PIE *aus- (2) "gold;" see aureate) + moulu "ground up," past participle of moudre "to grind," from Latin molere "to grind" (see mallet).
ornament (n.): early 13c., "an accessory," from Old French ornement "ornament, decoration," and directly from Latin ornamentum "apparatus, equipment, trappings; embellishment, decoration, trinket," from ornare "equip, adorn" (see ornate). Meaning "decoration, embellishment" in English is attested from late 14c. (also a secondary sense in classical Latin). Figurative use from 1550s.
ornament (v.): 1720, from ornament (n.). Middle English used ournen (late 14c.) in this sense, from Old French orner, from Latin ornare. Related: Ornamented; ornamenting.
ornamental (adj.): 1640s, partly formed in English from ornament (n.) + -al (1); partly from Latin ornamentalis, from ornamentum.
ornamentation (n.): 1839, noun of action from ornament (v.).
ornate (adj.): early 15c., from Latin ornatus "fitted out, furnished, supplied; adorned, decorated, embellished," past participle of ornare "adorn, fit out," from stem of ordo "order" (see order (n.)). Earliest reference is to literary style. Related: Ornately; ornateness.
ornery (adj.): 1816, American English dialectal contraction of ordinary (adj.). "Commonplace," hence "of poor quality, coarse, ugly." By c. 1860 the sense had evolved to "mean, cantankerous." Related: Orneriness.
ornitho-: before vowels ornith-, word-forming element meaning "bird, birds," from comb. form of Greek ornis (genitive ornithos) "a bird" (in Attic generally "domestic fowl"), often added to the specific name of the type of bird, from PIE *or- "large bird" (see erne).
ornithological (adj.): 1802, from ornithology + -ical. Related: Ornithologically.
ornithologist (n.): 1670s, from ornithology + -ist.
ornithology (n.): 1670s, from Modern Latin ornithologia (1590s); see ornitho- + -logy.
ornithopod (n.): 1888, from Modern Latin Ornithopoda (1881), from ornitho- + Greek podos, genitive of pous "foot," from PIE root *ped- (1) "a foot" (see foot (n.)).
ornithopter (n.): 1908, from French ornithoptère (1908), a machine designed to fly be mechanical flapping of wings, from ornitho- + Greek pteron "wing" (see ptero-). A mode of flight considered promising at least since Leonardo's day.
oro-: word-forming element meaning "mountain," from Greek oros "mountain" (see oread).
orogeny (n.): "mountain forming," 1890, from French orogénie; see oro- + -geny. Related: Orogenic.
orotund (adj.): 1792, from Latin ore rotundo "in well-rounded phrases," literally "with round mouth" (see ore rotundo).
The odd thing about the word is that its only currency, at least in its non-technical sense, is among those who should most abhor it, the people of sufficient education to realize its bad formation; it is at once a monstrosity in its form & a pedantry in its use. [Fowler]
orphan (v.): 1814, from orphan (n.). Related: Orphaned; orphaning.
orphan (n.): c. 1300, from Late Latin orphanus "parentless child" (source of Old French orfeno, Italian orfano), from Greek orphanos "orphaned, without parents, fatherless," literally "deprived," from orphos "bereft," from PIE *orbho- "bereft of father," also "deprived of free status," from root *orbh- "to change allegiance, to pass from one status to another" (source also of Hittite harb- "change allegiance," Latin orbus "bereft," Sanskrit arbhah "weak, child," Armenian orb "orphan," Old Irish orbe "heir," Old Church Slavonic rabu "slave," rabota "servitude" (see robot), Gothic arbja, German erbe, Old English ierfa "heir," Old High German arabeit, German Arbeit "work," Old Frisian arbed, Old English earfoð "hardship, suffering, trouble"). As an adjective from late 15c.

The Little Orphan Annie U.S. newspaper comic strip created by Harold Gray (1894-1968) debuted in 1924 in the New York "Daily News." Earlier it was the name (as Little Orphant Annie) of the character in James Whitcomb Riley's 1885 poem, originally titled "Elf Child":
LITTLE Orphant Annie's come to our house to stay,
An' wash the cups an' saucers up, an' brush the crumbs away,
An' shoo the chickens off the porch, an' dust the hearth, an' sweep,
An' make the fire, an' bake the bread, an' earn her board-an'-keep;
An' all us other childern, when the supper-things is done,
We set around the kitchen fire an' has the mostest fun
A-list'nin' to the witch-tales 'at Annie tells about,
An' the Gobble-uns 'at gits you
Ef you
Don't
Watch
Out!
orphanage (n.): 1570s, "condition of being an orphan," from orphan (n.) + -age. Meaning "home for orphans" is from 1865 (earlier was orphan house, 1711).
Orphic (adj.): 1670s, from Greek orphikos "pertaining to Orpheus," master musician of Thrace, son of Eagrus and Calliope, husband of Eurydice, whose name (of unknown origin) was associated with mystic doctrines. Related: Orphism.
orpiment (n.): late 13c., from Old French orpiment "arsenic trisulphide, yellow color," from Latin auripigmentum, from aurum "gold" (see aureate) + pigmentum "coloring matter, pigment, paint" (see pigment).
orrery (n.): 1713, invented c. 1713 by George Graham and made by instrument maker J. Rowley, who gave a copy to his patron, Charles Boyle, 4th Earl of Orrery (Cork) and named it in his honor.
Orson: masc. proper name, from French ourson, diminutive of ours "bear," from Latin ursus (see Arctic).
ort (n.): "remains of food left from a meal," mid-15c., probably cognate with early Dutch ooraete, Low German ort, from or-, privative prefix, + etan "to eat" (see eat (v.)). Perhaps from an unrecorded Old English word.
ortho-: before vowels orth-, word-forming element meaning "straight, upright, rectangular, regular; true, correct, proper," now mostly in scientific and technical compounds, from Greek ortho-, stem of orthos "straight, true, correct, regular," from PIE *eredh- "high" (source also of Sanskrit urdhvah "high, lofty, steep," Latin arduus "high, steep," Old Irish ard "high").
orthodontia (n.): 1849, from ortho- + Greek odon (genitive odontos) "tooth" (see tooth) + abstract noun ending -ia.
orthodontics (n.): 1909, from Modern Latin orthodontia + -ics.
orthodontist (n.): 1903; see orthodontia + -ist.
orthodox (adj.): mid-15c., of opinions, faith, from Late Latin orthodoxus, from Greek orthodoxos "having the right opinion," from orthos "right, true, straight" (see ortho-) + doxa "opinion, praise," from dokein "to seem," from PIE root *dek- "to take, accept" (see decent). As the name of the Eastern Church, first recorded in English 1772; in reference to a branch of Judaism, first recorded 1853.
orthodoxy (n.): 1620s, from French orthodoxie and directly from Late Latin orthodoxia, from late Greek orthodoxia "right opinion," noun of quality from orthodoxos (see orthodox).
orthogonal (adj.): 1570s, from French orthogonal, from orthogone, from Late Latin orthogonius, from Greek orthogonios "right-angled," from ortho- "straight" (see ortho-) + gonia "angle" (see -gon). Related: Orthogonally.
orthographic (adj.): 1660s, from orthography + -ic. Related: Orthographically.
orthography (n.): "correct or proper spelling," mid-15c., ortographie, from Middle French orthographie (Old French ortografie, 13c.), from Latin orthographia, from Greek orthographia "correct writing," from orthos "correct" (see ortho-) + root of graphein "to write" (see -graphy). Related: Orthographer.
orthopaedics (n.): chiefly British English spelling of orthopedics; for spelling, see pedo-. Related: Orthopaedic.
orthopedic (adj.): 1840, from French orthopédique, from orthopédie, coined by French physician Nicholas Andry (1658-1742), from Greek orthos "straight, correct" (see ortho-) + paideia "rearing of children," from pais (genitive paidos) "child" (see pedo-).
orthopedics (n.): 1853, from orthopedic. Also see -ics.
orthopedist (n.): 1853, from orthopedy (1840), from French orthopédie (18c.); see orthopedic + -ist.
orthopraxy (n.): 1840, from ortho- + Greek praxis "a doing, action, performance" (see praxis).
Errata -- Page 263, line 9 from bottom, for 'orthodoxy' read orthopraxy. This is a new coin from the mint of Dr. [Andrew] Wylie [of Bloomington College, Indiana], at least I have not before noticed it. Its etymology places it in a just contrast with orthodoxy: for if that consecrated word indicates thinking right, orthopraxy will legitimately import doing right, and hence, as Mr. Wylie says, orthopraxy in the last dread day will pass the divine ordeal incomparably better than orthodoxy. O! that a zeal for orthopraxy would transcend the zeal for orthodoxy! ["The Millennial Harbinger," vol. IV, no. VIII, Bethany, Va., August 1840]
Orwellian (adj.): 1950 (first attested in Mary McCarthy), from English author George Orwell (pseudonym of Eric Blair, 1903-1950), especially in reference to his novel "Nineteen Eighty-Four." Ironically, it has come to be used in reference to the totalitarian systems he satirized.
It is as if George Orwell had conceived the nightmare instead of analyzed it, helped to create it instead of helping to dispel its euphemistic thrall. [Clive James]
oryx (n.): late 14c., from Latin oryx, from Greek oryx (genitive orygos) "North African antelope with pointed horns, the digging animal," literally "pick-axe." Used in Greek and Latin bibles to render Hebrew tho, which early English Bibles misidentified as everything from a small hibernating animal to a wild bull.
os-: frequent form of ob- before -c- and -t- in words from Latin.
Osage: name of a group of Siouxan Indians originally from Missouri, 1690s, via French, from their self-designation Wazhazhe. The ornamental tree osage orange (Toxylon pomiferum), name first attested 1817, originally was found in their country.
Oscan (adj.): of or pertaining to the ancient people of southern Italy, 1590s, from Latin Osci, Opsci (plural) "Oscans," literally "worshippers of Ops," a harvest goddess, the name related to Latin ops (genitive opis) "abundance, plenty, wealth, riches," from PIE *op- (1) "to work, produce in abundance" (see opus).