twirler vs fireman

twirler and fireman both are nouns.

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

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

twirler (noun)	fireman (noun)
(baseball) the person who does the pitching	play in which children pretend to put out a fire
someone who twirls a baton	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