backup man vs reliever

backup man and reliever both are nouns.

Word	Noun	Adjective	Verb	Adverb
backup man	Yes	No	No	No
reliever	Yes	No	No	No

As nouns, backup man and reliever are synonyms defined as:

backup man and reliever: someone who takes the place of another (as when things get dangerous or difficult)

Other synonyms of backup man include backup, fill-in, relief, stand-in, substitute.

backup man (noun)	reliever (noun)
someone who takes the place of another (as when things get dangerous or difficult)	a pitcher who does not start the game
	someone who takes the place of another (as when things get dangerous or difficult)
	a person who reduces the intensity (e.g., of fears) and calms and pacifies