hitter vs slugger

hitter and slugger both are nouns.

Word	Noun	Adjective	Verb	Adverb
hitter	Yes	No	No	No
slugger	Yes	No	No	No

As nouns, hitter and slugger are synonyms defined as:

Other synonyms of hitter include batsman, batter.

hitter (noun)	slugger (noun)
(baseball) a ballplayer who is batting	(baseball) a ballplayer who is batting
someone who hits	a boxer noted for an ability to deliver hard punches