shooter vs gun

shooter and gun both are nouns.

Word	Noun	Adjective	Verb	Adverb
shooter	Yes	No	No	No
gun	Yes	No	Yes	No

As nouns, gun is a hyponym of shooter; that is, gun is a word with a more specific, narrower meaning than shooter:

shooter: a person who shoots (usually with respect to their ability to shoot)
gun: a person who shoots a gun (as regards their ability)

Other hyponyms of shooter include crack shot, marksman, sharpshooter, gunman, trapshooter.

As nouns, shooter and gun are synonyms defined as:

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

shooter (noun)	gun (noun)
a large marble used for shooting in the game of marbles	the discharge of a firearm as signal or as a salute in military ceremonies
a person who shoots (usually with respect to their ability to shoot)	a weapon that discharges a missile at high velocity (especially from a metal tube or barrel)
a professional killer who uses a gun	large but transportable armament
(sports) a player who drives or kicks a ball at the goal (or a basketball player who shoots at the basket)	a hand-operated pump that resembles a pistol; forces grease into parts of a machine
a gambler who throws dice in the game of craps	a pedal that controls the throttle valve
	a professional killer who uses a gun
	a person who shoots a gun (as regards their ability)

shooter (verb)	gun (verb)
	shoot with a gun