complaint vs murmur

complaint and murmur both are nouns.

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

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

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

complaint (noun)	murmur (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 schwa that is incidental to the pronunciation of a consonant
(civil law) the first pleading of the plaintiff setting out the facts on which the claim for relief is based	a low continuous indistinct sound; often accompanied by movement of the lips without the production of articulate speech
(criminal law) a pleading describing some wrong or offense	an abnormal sound of the heart; sometimes a sign of abnormal function of the heart valves
an often persistent bodily disorder or disease; a cause for complaining

complaint (verb)	murmur (verb)
	speak softly or indistinctly
	make complaining remarks or noises under one's breath