Reliever
Part of speech: noun
Definition: A relief pitcher. Someone who fills in for another.
Fireman
Part of speech: noun
Definition: A person who is skilled in the work of fighting fire.A fireman that is of the male sex (see usage note).A man who keeps the fire going underneath a steam boiler (originally, shoveling coal by hand), particularly on a railroad locomotive.By extension of the above, an assistant on any locomotive, whether steam-powered or not.A relief pitcher.