mutter vs muttering

mutter and muttering both are nouns.

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

As nouns, mutter and muttering are synonyms defined as:

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

As nouns, mutter and muttering are synonyms defined as:

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

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

mutter (noun)	muttering (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

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