hit man vs hired gun

hit man and hired gun both are nouns.

Word	Noun	Adjective	Verb	Adverb
hit man	Yes	No	No	No
hired gun	Yes	No	No	No

As nouns, hit man and hired gun are synonyms defined as:

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

hit man (noun)	hired gun (noun)
a professional killer who uses a gun	a professional killer who uses a gun