antagonist vs adversary

antagonist and adversary both are nouns.

Word	Noun	Adjective	Verb	Adverb
antagonist	Yes	No	No	No
adversary	Yes	No	No	No

As nouns, antagonist and adversary are synonyms defined as:

Other synonyms of antagonist include opponent, opposer, resister.

antagonist (noun)	adversary (noun)
a drug that neutralizes or counteracts the effects of another drug	someone who offers opposition
a muscle that relaxes while another contracts
someone who offers opposition