complain vs grumble

complain is not a noun while grumble is a noun.

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

As verbs, grumble is a hyponym of complain; that is, grumble is a word with a more specific, narrower meaning than complain:

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

complain (verb)	grumble (verb)
express complaints, discontent, displeasure, or unhappiness	make complaining remarks or noises under one's breath
make a formal accusation; bring a formal charge	show one's unhappiness or critical attitude
	to utter or emit low dull rumbling sounds
	make a low noise