Source : Webster's Revised Unabridged Dictionary (1913)

Antagonistic \An*tag`o*nis"tic\, Antagonistical
\An*tag`o*nis"tic*al\, a.
   Opposing in combat, combating; contending or acting against;
   as, antagonistic forces. -- {An*tag`o*nis"tic*al*ly}, adv.

         They were distinct, adverse, even antagonistic.
                                                  --Milman.

Source : WordNet®

antagonistic
     adj 1: indicating opposition or resistance [syn: {counter}]
     2: characterized by antagonism or antipathy; "slaves
        antagonistic to their masters"; "antipathetic factions
        within the party" [syn: {antipathetic}, {antipathetical}]
     3: arousing animosity or hostility; "his antagonizing
        brusqueness"; "Europe was antagonistic to the Unites
        States" [ant: {conciliatory}]
     4: used especially of drugs or muscles that counteract or
        neutralize each other's effect [syn: {incompatible}] [ant:
         {synergistic}]
     5: opposing or neutralizing or mitigating an effect by contrary
        action [syn: {counteractive}] [ant: {active}]
     6: incapable of harmonious association