complaint vs grumble

complaint and grumble both are nouns.

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

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

Other hyponyms of complaint include grievance, grumbling, murmur, murmuring, mutter, muttering, jeremiad, kvetch, pet peeve, whimper, whine.

complaint (noun)	grumble (noun)
an expression of grievance or resentment	a complaint uttered in a low and indistinct tone
(formerly) a loud cry (or repeated cries) of pain or rage or sorrow	a loud low dull continuous noise
(civil law) the first pleading of the plaintiff setting out the facts on which the claim for relief is based
(criminal law) a pleading describing some wrong or offense
an often persistent bodily disorder or disease; a cause for complaining

complaint (verb)	grumble (verb)
	make complaining remarks or noises under one's breath
	show one's unhappiness or critical attitude
	to utter or emit low dull rumbling sounds
	make a low noise