Source : Webster's Revised Unabridged Dictionary (1913)

Antagonism \An*tag"o*nism\, n. [Gr. ?, fr. ? to struggle
   against; ? against + ? to contend or struggle, ? contest: cf.
   F. antagonisme. See {Agony}.]
   Opposition of action; counteraction or contrariety of things
   or principles.

   Note: We speak of antagonism between two things, to or
         against a thing, and sometimes with a thing.

Source : WordNet®

antagonism
     n 1: a state of deep-seated ill-will [syn: {hostility}, {enmity}]
     2: the relation between opposing principles or forces or
        factors; "the inherent antagonism of capitalism and
        socialism"
     3: an actively expressed feeling of dislike and hostility
     4: (biochemistry) interference in or inhibition of the
        physiological action of a chemical substance by another
        having a similar structure