fireman vs fire warden

fireman and fire warden both are nouns.

Word	Noun	Adjective	Verb	Adverb
fireman	Yes	No	No	No
fire warden	Yes	No	No	No

As nouns, fire warden is a hyponym of fireman; that is, fire warden is a word with a more specific, narrower meaning than fireman:

fireman: a member of a fire department who tries to extinguish fires
fire warden: an official who is responsible for managing and protecting an area of forest

Other hyponyms of fireman include fire chief, fire marshal, forest fire fighter, ranger.

fireman (noun)	fire warden (noun)
play in which children pretend to put out a fire	an official who is responsible for managing and protecting an area of forest
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