mutter vs mumble

mutter and mumble both are nouns.

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

As verbs, mutter and mumble are synonyms defined as:

Other synonyms of mutter include maunder, mussitate.

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

mutter (verb)	mumble (verb)
make complaining remarks or noises under one's breath	talk indistinctly; usually in a low voice
talk indistinctly; usually in a low voice	grind with the gums; chew without teeth and with great difficulty