slugger vs pinch hitter

slugger and pinch hitter both are nouns.

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

As nouns, pinch hitter is a hyponym of slugger; that is, pinch hitter is a word with a more specific, narrower meaning than slugger:

Other hyponyms of slugger include bunter, designated hitter, switch-hitter, whiffer.

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