The Collaborative International Dictionary of English v.0.48:

Enantiosis \E*nan`ti*o"sis\, n. [NL., fr. Gr. ? contradiction,
   fr. 'enanti`os opposite.] (Rhet.)
   A figure of speech by which what is to be understood
   affirmatively is stated negatively, and the contrary;
   affirmation by contraries.
   [1913 Webster]