mutter vs mutterer

mutter and mutterer both are nouns.

Word	Noun	Adjective	Verb	Adverb
mutter	Yes	No	Yes	No
mutterer	Yes	No	No	No

mutter (noun)	mutterer (noun)
a complaint uttered in a low and indistinct tone	a person who speaks softly and indistinctly
a low continuous indistinct sound; often accompanied by movement of the lips without the production of articulate speech

mutter (verb)	mutterer (verb)
make complaining remarks or noises under one's breath
talk indistinctly; usually in a low voice