Are yams and sweet potatoes the same?
1650s, from Greek oxymoron, noun use of neuter of oxymoros (adj.) "pointedly foolish," from oxys "sharp" (see acrid) + moros "stupid" (see moron). Rhetorical figure by which contradictory terms are conjoined so as to give point to the statement or expression; the word itself is an illustration of the thing. Now often used loosely to mean "contradiction in terms." Related: Oxymoronic.
A rhetorical device in which two seemingly contradictory words are used together for effect: “She is just a poor little rich girl.”