Source : Webster's Revised Unabridged Dictionary (1913)

Obversion \Ob*ver"sion\, n. [L. obversio a turning towards.]
   1. The act of turning toward or downward.

   2. (Logic) The act of immediate inference, by which we deny
      the opposite of anything which has been affirmed; as, all
      men are mortal; then, by obversion, no men are immortal.
      This is also described as ``immediate inference by
      privative conception.'' --Bain.