pinch hitter vs slugger

pinch hitter and slugger both are nouns.

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

As nouns, slugger is a hypernym of pinch hitter; that is, slugger is a word with a broader meaning than pinch hitter:

Other hypernyms of pinch hitter include batsman, batter, hitter, reserve, second-stringer, substitute.

pinch hitter (noun)	slugger (noun)
(baseball) a substitute for the regular batter	(baseball) a ballplayer who is batting
	a boxer noted for an ability to deliver hard punches