muttering vs mussitation

muttering and mussitation both are nouns.

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

As nouns, muttering and mussitation are synonyms defined as:

muttering and mussitation: 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, mutter.

muttering (noun)	mussitation (noun)
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