murmur vs murmurer

murmur and murmurer both are nouns.

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

murmur (noun)	murmurer (noun)
a complaint uttered in a low and indistinct tone	a person who speaks softly and indistinctly
a schwa that is incidental to the pronunciation of a consonant
a low continuous indistinct sound; often accompanied by movement of the lips without the production of articulate speech
an abnormal sound of the heart; sometimes a sign of abnormal function of the heart valves

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