Source : Webster's Revised Unabridged Dictionary (1913)

Antagonize \An*tag"o*nize\, v. t. [imp. & p. p. {Antagonized};
   p. pr. & vb. n. {Antagonozing}.] [Gr. ?. See {Antagonism}.]
   To contend with; to oppose actively; to counteract.

Antagonize \An*tag"o*nize\, v. i.
   To act in opposition.

Source : WordNet®

antagonize
     v 1: provoke the hostility of; "Don't antagonize your boss" [syn:
           {antagonise}]
     2: act in opposition to [syn: {antagonise}, {counteract}]