[n] two words that express opposing concepts; "to him the opposite of gay was depressed"
opposite - (3 syllables), opposite word - (4 syllables)
\An"to*nym\, n. [Gr. ? a word used in substitution for another; ? + ?, ?, a word.] A word of opposite meaning; a counterterm; -- used as a correlative of synonym. [R.] --C. J. Smith.