antiphrasis n.

word-forming element of Greek origin meaning "against, opposed to, opposite of, instead," shortened to ant- before vowels and -h-, from Old French anti- and directly from Latin anti-, from Greek anti (prep.) "over, against, opposite; instead, in the place of; as good as; at the price of; for the sake of; compared with; in opposition to; in return; counter-," from PIE *anti "against," also "in front of, before" (from root *ant- "front, forehead," with derivatives meaning "in front of, before"), which became anti- in Italian (hence antipasto) and French.

It is cognate with Sanskrit anti "over, against," and Old English and- (the first element in answer). A common compounding element in Greek, in some combinations it became anth- for euphonic reasons. It appears in some words in Middle English but was not commonly used in English word formations until modern times. In a few English words (anticipate, antique) it represents Latin ante.

In noun compounds where it has the sense of "opposed to, opposite" (Antichrist, anti-communist) the accent remains on the anti-; in adjectives where it retains its old prepositional sense "against, opposed to," the accent remains on the other element (anti-Christian, anti-slavery).

1520s, "manner or style of expression," also "brief expression with some unity; two or more words expressing what is practically a single notion," from Late Latin phrasis "diction," from Greek phrasis "speech, way of speaking, enunciation, phraseology," from phrazein "to tell, declare, indicate, point out, show, inform," also passively (phrazomai), "indicate to oneself, think or muse upon, consider; think up, contrive; suppose, believe, imagine; perceive, observe."

The Greek verb is of uncertain origin; perhaps it is connected with phrenes "wits, senses, sanity," phrēn "the mind, the heart," literally "midriff, diaphragm" (see phreno-). The musical sense of "a short and somewhat independent passage from a piece" is from 1789. Phrase-book "collection of expressions peculiar to a language" is by 1590s.