Source : Webster's Revised Unabridged Dictionary (1913)

Oxymoron \Ox`y*mo"ron\, n. [NL., fr. Gr. ???, fr. ??? pointedly
   foolish; ??? sharp + ??? foolish.] (Rhet.)
   A figure in which an epithet of a contrary signification is
   added to a word; e. g., cruel kindness; laborious idleness.

Source : WordNet®

oxymoron
     n : conjoining contradictory terms (as in `deafening silence')
     [also: {oxymora} (pl)]