opposer vs antagonist

opposer and antagonist both are nouns.

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

As nouns, opposer and antagonist are synonyms defined as:

Other synonyms of opposer include adversary, opponent, resister.

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