firefighter vs fire fighter

firefighter and fire fighter both are nouns.

Word	Noun	Adjective	Verb	Adverb
firefighter	Yes	No	No	No
fire fighter	Yes	No	No	No

As nouns, firefighter and fire fighter are synonyms defined as:

firefighter and fire fighter: a member of a fire department who tries to extinguish fires

Other synonyms of firefighter include fire-eater, fireman.

firefighter (noun)	fire fighter (noun)
a member of a fire department who tries to extinguish fires	a member of a fire department who tries to extinguish fires