-ocracy Look up -ocracy at Dictionary.com
word-forming element; -cracy with a connective -o-.
-oholic Look up -oholic at Dictionary.com
word-forming element abstracted from alcoholic (q.v.); also see -aholic, which has tended to replace it in word formation.
-oid Look up -oid at Dictionary.com
word-forming element meaning "like, like that of, thing like a ______," from Latinized form of Greek -oeides, from eidos "form," related to idein "to see," eidenai "to know;" literally "to see," from PIE *weid-es-, from root *weid- "to see, to know" (see vision). The -o- is connective or a stem vowel from the previous element.
-oidal Look up -oidal at Dictionary.com
word-forming element making adjectives from nouns in -oid; see -oid + -al (1).
-ol Look up -ol at Dictionary.com
word-forming element in chemistry, variously representing alcohol, phenol, or in some cases Latin oleum "oil" (see oil (n.)).
-ola Look up -ola at Dictionary.com
commercial suffix, probably originally in pianola (q.v.).
-ologist Look up -ologist at Dictionary.com
word-forming element; see -ology + -ist.
-ology Look up -ology at Dictionary.com
word-forming element indicating "branch of knowledge, science," now the usual form of -logy. Originally used c.1800 in nonce formations (commonsensology, etc.), it gained legitimacy by influence of the proper formation in geology, mythology, etc., where the -o- is a stem vowel in the previous element.
-oma Look up -oma at Dictionary.com
word-forming element, from Greek -oma, with lengthened stem vowel + -ma, suffix forming neuter nouns and nouns that indicate result of verbal action (equivalent of Latin -men); especially taken in medical use as "morbid growth, tumor," based on sarcoma, carcinoma.
-on Look up -on at Dictionary.com
subatomic particle suffix, from ion.
-one Look up -one at Dictionary.com
chemical suffix, from Greek -one, female patronymic (as in anemone, "daughter of the wind," from anemos); in chemical use denoting a "weaker" derivative. Its use in forming acetone (1830s) gave rise to the specialized chemical sense.
-oon Look up -oon at Dictionary.com
spelling conventional in 15c.-17c. English to add emphasis to borrowed French nouns ending in stressed -on; also used to represent Italian -one, Spanish ón; all from Latin -onem. Used in rare cases to form English words, such as spittoon, octaroon.
-or Look up -or at Dictionary.com
word-forming element making nouns of quality, state, or condition, from Middle English -our, from Old French -our (Modern French -eur), from Latin -orem (nominative -or), a suffix added to pp. verbal stems. Also in some cases from Latin -atorem (nominative -ator).

In U.S., via Noah Webster, -or is nearly universal (but not in glamour, curious, generous), while in Britain -our is used in most cases (but with many exceptions: author, error, senator, ancestor, horror etc.). The -our form predominated after c.1300, but Mencken reports that the first three folios of Shakespeare's plays used both spellings indiscriminately and with equal frequency; only in the Fourth Folio of 1685 does -our become consistent.

A partial revival of -or on the Latin model took place from 16c. (governour began to lose its -u- 16c. and it was gone by 19c.), and also among phonetic spellers in both England and America (John Wesley wrote that -or was "a fashionable impropriety" in England in 1791).

Webster criticized the habit of deleting -u- in -our words in his first speller ("A Grammatical Institute of the English Language," commonly called the Blue-Black Speller) in 1783. His own deletion of the -u- began with the revision of 1804, and was enshrined in the influential "Comprehensive Dictionary of the English Language" (1806), which also established in the U.S. -ic for British -ick and -er for -re, along with many other attempts at reformed spelling which never caught on (such as masheen for machine). His attempt to justify them on the grounds of etymology and the custom of great writers does not hold up.

Fowler notes the British drop the -u- when forming adjectives ending in -orous (humorous) and derivatives in -ation and -ize, in which cases the Latin origin is respected (such as vaporize). When the Americans began to consistently spell it one way, however, the British reflexively hardened their insistence on the other. "The American abolition of -our in such words as honour and favour has probably retarded rather than quickened English progress in the same direction." [Fowler]
-ory Look up -ory at Dictionary.com
adjective and noun suffix, "having to do with, characterized by, tending to, place for," from Middle English -orie, from Old North French -ory, -orie (Old French -oir, -oire), from Latin -orius, -oria, -orium.

Latin adjectives in -orius, according to "An Etymological Dictionary of the French Language," tended to "indicate a quality proper to the action accomplished by the agent; as oratorius from orator; laudatorius from laudator. The neuter of these adjectives was early employed as a substantive, and usually denoted the place of residence of the agent or the instrument that he uses; as praetorium from praetor; dormitorium from dormitor; auditorium, dolatorium.

"These newer words, already frequent under the Empire, became exceedingly numerous at a later time, especially in ecclesiastical and scholastic Latin; as purgatorium, refectorium, laboratorium, observatorium, &c." [transl. G.W. Kitchin, Oxford, 1878]
-ose (2) Look up -ose at Dictionary.com
standard ending in chemical names of sugars, originally simply a noun-forming suffix, taken up by French chemists mid-19c.; it has no etymological connection with sugar. It appears around the same time in two chemical names, cellulose, which would owe it to the French suffix, and glucose, where it would be a natural result from the Greek original. Flood favors origin from glucose.
-ose (1) Look up -ose at Dictionary.com
word-forming element used to make adjectives from nouns, with the meaning "full of, abounding in, having qualities of," from Latin -osus (see -ous).
-osis Look up -osis at Dictionary.com
word-forming element expressing state or condition, in medical terminology denoting "a state of disease," from Latin -osis and directly from Greek -osis, formed from the aorist of verbs ending in -o. It corresponds to Latin -atio.
-osity Look up -osity at Dictionary.com
word-forming element making nouns from adjectives in -ous, -ose (1); from French -osité, from Latin -ositatem (nominative -ositas), properly -ose + -ity.
-our Look up -our at Dictionary.com
see -or.
-ous Look up -ous at Dictionary.com
word-forming element making adjectives from nouns, meaning "having, full of, having to do with, doing, inclined to," from Old French -ous, -eux, from Latin -osus (compare -ose (1)). In chemistry, "having a lower valence than forms expressed in -ic."
o Look up o at Dictionary.com
interjection of fear, surprise, admiration, etc.; see oh.
O Look up O at Dictionary.com
blood type, 1926, originally "zero," denoting absence of A and B agglutinogens.
O' Look up O' at Dictionary.com
as a prefix in Irish names, from Irish ó, ua (Old Irish au) "descendant."
o'clock (adj.) Look up o'clock at Dictionary.com
c.1720, abbreviation of of the clock (1640s), from Middle English of the clokke (late 14c.). Use of clock hand positions to describe vector directions or angles is from late 18c.
o'er Look up o'er at Dictionary.com
poetic contraction of over.
O.D. Look up O.D. at Dictionary.com
abbreviation of overdose, attested from 1960.
oaf (n.) Look up oaf at Dictionary.com
1620s, auf, oph (modern form from 1630s), "a changeling; a foolish child left by the fairies" [Johnson], from a Scandinavian source such as Norwegian alfr "silly person," in Old Norse "elf" (see elf). Hence, "a misbegotten, deformed idiot." Until recently, some dictionaries still gave the plural as oaves.
oafish (adj.) Look up oafish at Dictionary.com
1610s, from oaf + -ish. Related: Oafishly; oafishness.
oak (n.) Look up oak at Dictionary.com
Old English ac "oak tree," from Proto-Germanic *aiks (cognates: Old Norse eik, Old Saxon and Old Frisian ek, Middle Dutch eike, Dutch eik, Old High German eih, German Eiche), of uncertain origin with no certain cognates outside Germanic.

The usual Indo-European base for "oak" (*deru-) has become Modern English tree (n.); likewise in Greek and Celtic words for "oak" are from the Indo-European root for "tree," probably reflecting the importance of the oak to ancient Indo-Europeans. The Old Norse form was eik, but as there were no oaks in Iceland the word came to be used there for "tree" in general. Used in Biblical translations to render Hebrew elah (probably usually "terebinth tree") and four other words.
oaken (adj.) Look up oaken at Dictionary.com
"made of, or consisting of, oak," late 12c., from oak + -en (2).
oakum (n.) Look up oakum at Dictionary.com
"loose fiber obtained from taking apart old hemp ropes," early 15c., from Old English acumba "tow, oakum, flax fibers separated by combing," literally "what is combed out," from Proto-Germanic *us-kambon (source of Old High German achambi); first element cognate with Old English a- "away, out, off;" second element from stem of cemban "to comb," from camb "a comb;" from PIE *gembh- "tooth, nail" (see comb (n.)).
oar (n.) Look up oar at Dictionary.com
Old English ar "oar," from Proto-Germanic *airo (cognates: Old Norse ar, Danish aare, Swedish åra), of unknown origin; perhaps related to Latin remus "oar," Greek eretes "rower," eretmos "oar."
oarlock (n.) Look up oarlock at Dictionary.com
mid-14c., from oar + lock (n.1).
oasis (n.) Look up oasis at Dictionary.com
1610s, from French oasis (18c.) and directly from Late Latin oasis, from Greek oasis, probably from Hamitic (compare Coptic wahe, ouahe "oasis," properly "dwelling place," from ouih "dwell"). The same Egyptian source produced Arabic wahah.
oat (n.) Look up oat at Dictionary.com
Old English ate (plural atan) "grain of the oat plant, wild oats," of uncertain origin, possibly from Old Norse eitill "nodule," denoting a single grain, of unknown origin. The English word has cognates in Frisian and some Dutch dialects. Famously defined by Johnson as, "A grain, which in England is generally given to horses, but in Scotland supports the people."

The usual Germanic name is derived from Proto-Germanic *khabran (cognates: Old Norse hafri, Dutch haver, source of haversack). Wild oats, "crop that one will regret sowing," is first attested 1560s, in reference to the folly of sowing these instead of good grain.
That wilfull and vnruly age, which lacketh rypenes and discretion, and (as wee saye) hath not sowed all theyr wyeld Oates. [Thomas Newton, "Lemnie's Touchstone of complexions," 1576]



Fred Sanford: I still want to sow some wild oats!
Lamont Sanford: At your age, you don't have no wild oats, you got shredded wheat.
["Sanford and Son"]
Hence, to feel (one's) oats "be lively," 1831, originally American English.
oater (n.) Look up oater at Dictionary.com
Western film, "horse opera," 1946, from oat, as the typical food of horses.
oath (n.) Look up oath at Dictionary.com
Old English "oath, judicial swearing, solemn appeal to deity in witness of truth or a promise," from Proto-Germanic *aithaz (cognates: Old Norse eiðr, Swedish ed, Old Saxon, Old Frisian eth, Middle Dutch eet, Dutch eed, German eid, Gothic aiþs "oath"), from PIE *oi-to- "an oath" (cognates: Old Irish oeth "oath"). Common to Celtic and Germanic, possibly a loan-word from one to the other, but the history is obscure. In reference to careless invocations of divinity, from late 12c.
oatmeal (n.) Look up oatmeal at Dictionary.com
late 14c., from oat + Middle English mele (see meal (n.2)).
ob- Look up ob- at Dictionary.com
prefix meaning "toward, against, across, down," also used as an intensive, from Latin ob "toward, to, over against, in the way of, by reason of, about, before, in front of," from PIE root *epi, also *opi "near, against" (see epi-).
Obadiah Look up Obadiah at Dictionary.com
masc. proper name, fourth of the Twelve Prophets of the Old Testament, from Hebrew Obhadyah, literally "servant of the Lord," from abhadh "he served, worshipped," related to Arabic 'abada "he served," 'abd "slave, worshipper."
obbligato (adj.) Look up obbligato at Dictionary.com
musical instruction, 1724, from Italian obbligato, literally "obligated," from Latin obligatus, past participle of obligare "to bind" (see oblige). In reference to a necessary accompaniment by a single instrument.
obduracy (n.) Look up obduracy at Dictionary.com
"stubbornness," 1590s, from obdurate + -cy.
obdurate (adj.) Look up obdurate at Dictionary.com
mid-15c., "stubborn; hardened," from Latin obduratus "hardened," past participle of obdurare "be hard, hold out, persist, endure," from ob "against" (see ob-) + durare "harden, render hard," from durus "hard" (see endure). Related: Obdurately.
obduration (n.) Look up obduration at Dictionary.com
c.1400, "hard-heartedness," from Latin obdurationem (nominative obduratio), noun of state from past participle stem of obdurare (see obdurate).
obeah (n.) Look up obeah at Dictionary.com
"sorcery, witchcraft" among blacks in Africa and the W.Indies, 1760, from a West African word, such as Efik (southern Nigeria) ubio "a thing or mixture left as a charm to cause sickness or death," Twi ebayifo "witch, wizard, sorcerer."
obedience (n.) Look up obedience at Dictionary.com
c.1200, "submission to a higher power or authority," from Old French obedience "obedience, submission" (12c.) and directly from Latin oboedientia "obedience," noun of quality from oboedientem (nominative oboediens); see obedient. In reference to dog training from 1930.
obedient (adj.) Look up obedient at Dictionary.com
c.1200, from Old French obedient "obedient" (11c.), from Latin oboedientem (nominative oboediens), present participle of oboedire "to obey" (see obey). Related: Obediently.
obeisance (n.) Look up obeisance at Dictionary.com
late 14c., "act or fact of obeying," from Old French obeissance "obedience, service, feudal duty" (13c.), from obeissant, present participle of obeir "obey," from Latin oboedire (see obey). Sense in English altered late 14c. to "bending or prostration of the body as a gesture of submission or respect" by confusion with abaisance. Related: Obeisant.
obelisk (n.) Look up obelisk at Dictionary.com
"rectangular stone column tapering at the top," 1560s, from Middle French obélisque (16c.) and directly from Latin obeliscus "obelisk, small spit," from Greek obeliskos "small spit, obelisk, leg of a compass," diminutive of obelos "a spit, pointed pillar, needle." Related: Obeliskine.
Oberon Look up Oberon at Dictionary.com
king of the faeries and husband of Titania in medieval lore, from French Obéron, from Old French Auberon, perhaps from a Germanic source related to elf.