antagonist vs dueler

antagonist and dueler both are nouns.

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

As nouns, dueler is a hyponym of antagonist; that is, dueler is a word with a more specific, narrower meaning than antagonist:

Other hyponyms of antagonist include duelist, dueller, duellist, enemy, foe, foeman, opposition, Luddite, withstander.

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