oxymoron (n.)

in rhetoric, "a figure conjoining words or terms apparently contradictory so as to give point to the statement or expression," 1650s, from Greek oxymōron, noun use of neuter of oxymōros (adj.) "pointedly foolish," from oxys "sharp, pointed" (from PIE root *ak- "be sharp, rise (out) to a point, pierce") + mōros "stupid" (see moron). The word itself is an illustration of the thing. Now often used loosely to mean "contradiction in terms." Related: Oxymoronic.