gunslinger vs hitman

gunslinger and hitman both are nouns.

Word	Noun	Adjective	Verb	Adverb
gunslinger	Yes	No	No	No
hitman	Yes	No	No	No

As nouns, gunslinger and hitman are synonyms defined as:

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

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