fireman vs ranger

fireman and ranger both are nouns.

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

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

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

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

fireman (noun)	ranger (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 member of a military unit trained as shock troops for hit-and-run raids
a laborer who tends fires (as on a coal-fired train or steamship)
a pitcher who does not start the game