combatant vs doer

combatant and doer both are nouns.

Word	Noun	Adjective	Verb	Adverb
combatant	Yes	Yes	No	No
doer	Yes	No	No	No

As nouns, doer is a hypernym of combatant; that is, doer is a word with a broader meaning than combatant:

Other hypernyms of combatant include actor, worker.

combatant (noun)	doer (noun)
someone who fights (or is fighting)	a person who acts and gets things done

combatant (adjective)	doer (adjective)
engaging in or ready for combat