gunman vs hit man

gunman and hit man both are nouns.

Word	Noun	Adjective	Verb	Adverb
gunman	Yes	No	No	No
hit man	Yes	No	No	No

As nouns, gunman and hit man are synonyms defined as:

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

gunman (noun)	hit man (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)