murmur vs murmurous

murmur is a noun but murmurous is not a noun.

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

murmur (noun)	murmurous (noun)
a complaint uttered in a low and indistinct tone
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 (adjective)	murmurous (adjective)
	characterized by soft sounds

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