gun for hire vs gunslinger

gun for hire and gunslinger both are nouns.

Word	Noun	Adjective	Verb	Adverb
gun for hire	Yes	No	No	No
gunslinger	Yes	No	No	No

As nouns, gun for hire and gunslinger are synonyms defined as:

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

gun for hire (noun)	gunslinger (noun)
a professional killer who uses a gun	a professional killer who uses a gun