grumble vs emit

grumble is a noun but emit is not a noun.

Word	Noun	Adjective	Verb	Adverb
grumble	Yes	No	Yes	No
emit	No	No	Yes	No

As verbs, emit is a hypernym of grumble; that is, emit is a word with a broader meaning than grumble:

Other hypernyms of grumble include let loose, let out, utter.

grumble (noun)	emit (noun)
a complaint uttered in a low and indistinct tone
a loud low dull continuous noise

grumble (verb)	emit (verb)
make complaining remarks or noises under one's breath	expel (gases or odors)
show one's unhappiness or critical attitude	express audibly; utter sounds (not necessarily words)
to utter or emit low dull rumbling sounds	give off, send forth, or discharge; as of light, heat, or radiation, vapor, etc.
make a low noise