"utopia," from title of a book published 1872 by British author Samuel Butler, a partial reversal of nowhere.
spelled-out form of K.O. (for knockout in the pugilism sense), from 1923. Also used in 1920s as a slang reversal of OK.
German prefix "denoting destruction, reversal, or completion" [Watkins], from Proto-Germanic *fer-, *far-, from PIE root *per- (1) "forward," hence "through."
prefix of reversal, deprivation, or removal (as in unhand, undo, unbutton), Old English on-, un-, from Proto-Germanic *andi- (source also of Old Saxon ant-, Old Norse and-, Dutch ont-, Old High German ant-, German ent-, Gothic and- "against"), from PIE *anti "facing opposite, near, in front of, before, against" (from PIE root *ant- "front, forehead," with derivatives meaning "in front of, before").
More or less confused with un- (1) through similarity in the notions of "negation" and "reversal;" an adjective such as unlocked might represent "not locked" (un- (1)) or the past tense of unlock (un- (2)).
also set-back, 1670s, "reversal, check to progress," from the verbal phrase, attested mid-15c. as "withhold;" see set (v.) + back (adv.). Backset (1721) is used in the same sense. The meaning "space between a building and a property line or roadway" is from 1916. To set (someone) back "cost" (a certain sum of money) is from 1900.
early 15c., "rejected as worthless," from Late Latin reprobatus, past participle of reprobare "disapprove, reject, condemn," from Latin re- "back, again," here perhaps indicating "opposite of, reversal of previous condition" (see re-) + probare "prove to be worthy" (see probate (n.)). The meaning "abandoned in character, morally depraved, unprincipled" is by 1650s.
c. 1300, repreven, repruve, reproeven, "accuse, charge as a fault," from Old French reprover "accuse, blame" (12c.), from Late Latin reprobare "disapprove, reject, condemn," from Latin re- "opposite of, reversal of previous condition" (see re-) + probare "prove to be worthy" (see probate (n.)).
From mid-14c. as "deliver a rebuke, admonish;" late 14c. as "disapprove, condemn, find fault with." Related: Reproved; reproving; reprovable.