marksman vs shooter

marksman and shooter both are nouns.

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

As nouns, shooter is a hypernym of marksman; that is, shooter is a word with a broader meaning than marksman:

marksman: someone skilled in shooting
shooter: a person who shoots (usually with respect to their ability to shoot)

Other hypernyms of marksman include shot.

marksman (noun)	shooter (noun)
someone skilled in shooting	a large marble used for shooting in the game of marbles
	a person who shoots (usually with respect to their ability to shoot)
	a professional killer who uses a gun
	(sports) a player who drives or kicks a ball at the goal (or a basketball player who shoots at the basket)
	a gambler who throws dice in the game of craps