fire chief vs fireman

fire chief and fireman both are nouns.

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

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

Other hypernyms of fire chief include fire-eater, fire fighter, firefighter.

fire chief (noun)	fireman (noun)
the head of a fire department	play in which children pretend to put out a fire
	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