hired gun vs hitman

hired gun and hitman both are nouns.

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

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

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

hired gun (noun)	hitman (noun)
a professional killer who uses a gun	a professional killer who uses a gun