D defs.my
Entry 2 senses Webster, 1913

Obversion

/(ŏb*vẽr"shŭn)/ · Ob·ver·sion · IPA
01 n. The act of turning toward or downward.
  1. 1.
    The act of turning toward or downward.
  2. 2.
    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.”(Logic)