fireman vs guardian

fireman and guardian both are nouns.

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

As nouns, guardian is a hypernym of fireman; that is, guardian is a word with a broader meaning than fireman:

Other hypernyms of fireman include defender, protector, shielder.

fireman (noun)	guardian (noun)
play in which children pretend to put out a fire	a person who cares for persons or property
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