fire-eater vs grump

fire-eater and grump both are nouns.

Word	Noun	Adjective	Verb	Adverb
fire-eater	Yes	No	No	No
grump	Yes	No	No	No

As nouns, grump is a hypernym of fire-eater; that is, grump is a word with a broader meaning than fire-eater:

Other hypernyms of fire-eater include churl, crank, crosspatch, grouch.

fire-eater (noun)	grump (noun)
a performer who pretends to swallow fire	a bad-tempered person
a belligerent grouch
a member of a fire department who tries to extinguish fires