reliever vs fireman

reliever and fireman both are nouns.

Word	Noun	Adjective	Verb	Adverb
reliever	Yes	No	No	No
fireman	Yes	No	No	No

As nouns, reliever and fireman are synonyms defined as:

Other synonyms of reliever include relief pitcher.

reliever (noun)	fireman (noun)
a pitcher who does not start the game	play in which children pretend to put out a fire
someone who takes the place of another (as when things get dangerous or difficult)	a member of a fire department who tries to extinguish fires
a person who reduces the intensity (e.g., of fears) and calms and pacifies	a laborer who tends fires (as on a coal-fired train or steamship)
	a pitcher who does not start the game