antihero vs protagonist

antihero and protagonist both are nouns.

Word	Noun	Adjective	Verb	Adverb
antihero	Yes	No	No	No
protagonist	Yes	No	No	No

As nouns, protagonist is a hypernym of antihero; that is, protagonist is a word with a broader meaning than antihero:

antihero: a protagonist who lacks the characteristics that would make him a hero (or her a heroine)
protagonist: the principal character in a work of fiction

Other hypernyms of antihero include agonist.

antihero (noun)	protagonist (noun)
a protagonist who lacks the characteristics that would make him a hero (or her a heroine)	a person who backs a politician or a team etc.
	the principal character in a work of fiction