hitter vs pinch hitter

hitter and pinch hitter both are nouns.

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

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

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

hitter (noun)	pinch hitter (noun)
(baseball) a ballplayer who is batting	(baseball) a substitute for the regular batter
someone who hits