1.Definition: arousing animosity or hostility

"His antagonistic brusqueness", "Europe was antagonistic to the Unites States"

2.Definition: characterized by antagonism or antipathy

"Slaves antagonistic to their masters"

Related Adjective(s):antipathetic, antipathetical

3.Definition: incapable of harmonious association

4.Definition: indicating opposition or resistance

Related Adjective(s):counter

5.Definition: used especially of drugs or muscles that counteract or neutralize each other's effect

Related Adjective(s):incompatible