muttering vs mutter

muttering and mutter both are nouns.

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

As nouns, muttering and mutter are synonyms defined as:

Other synonyms of muttering include grumble, grumbling, murmur, murmuring.

As nouns, muttering and mutter are synonyms defined as:

muttering and mutter: a low continuous indistinct sound; often accompanied by movement of the lips without the production of articulate speech

Other synonyms of muttering include murmur, murmuration, murmuring, mussitation.

muttering (noun)	mutter (noun)
a complaint uttered in a low and indistinct tone	a complaint uttered in a low and indistinct tone
a low continuous indistinct sound; often accompanied by movement of the lips without the production of articulate speech	a low continuous indistinct sound; often accompanied by movement of the lips without the production of articulate speech

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