hired gun vs gunman

hired gun and gunman both are nouns.

Word	Noun	Adjective	Verb	Adverb
hired gun	Yes	No	No	No
gunman	Yes	No	No	No

As nouns, hired gun and gunman are synonyms defined as:

Other synonyms of hired gun include gun, gun for hire, gunslinger, hit man, hitman, shooter, torpedo, triggerman.

hired gun (noun)	gunman (noun)
a professional killer who uses a gun	a professional killer who uses a gun
	a person who shoots a gun (as regards their ability)