relief pitcher vs pitcher

relief pitcher and pitcher both are nouns.

Word	Noun	Adjective	Verb	Adverb
relief pitcher	Yes	No	No	No
pitcher	Yes	No	No	No

As nouns, pitcher is a hypernym of relief pitcher; that is, pitcher is a word with a broader meaning than relief pitcher:

Other hypernyms of relief pitcher include hurler, twirler.

relief pitcher (noun)	pitcher (noun)
a pitcher who does not start the game	the position on a baseball team of the player who throws the ball for a batter to try to hit
	an open vessel with a handle and a spout for pouring
	(baseball) the person who does the pitching
	(botany) a leaf that is modified in such a way as to resemble a pitcher or ewer
	the quantity contained in a pitcher