relief pitcher vs fireman

relief pitcher and fireman both are nouns.

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

As nouns, relief pitcher and fireman are synonyms defined as:

Other synonyms of relief pitcher include reliever.

relief pitcher (noun)	fireman (noun)
a pitcher who does not start the game	play in which children pretend to put out a fire
	a member of a fire department who tries to extinguish fires
	a laborer who tends fires (as on a coal-fired train or steamship)
	a pitcher who does not start the game