duellist vs antagonist

duellist and antagonist both are nouns.

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

As nouns, antagonist is a hypernym of duellist; that is, antagonist is a word with a broader meaning than duellist:

Other hypernyms of duellist include adversary, opponent, opposer, resister.

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