Source : Webster's Revised Unabridged Dictionary (1913)

Contraposition \Con"tra*po*si"tion\, n. [Pref. contra- +
   position: cf. f. conterposition.]
   1. A placing over against; opposite position. [Obs.] --F.
      Potter.

   2. (Logic) A so-called immediate inference which consists in
      denying the original subject of the contradictory
      predicate; e.g.: Every S is P; therefore, no Not-P is S.