mutter vs mussitate

mutter is a noun but mussitate is not a noun.

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

As verbs, mutter and mussitate are synonyms defined as:

Other synonyms of mutter include maunder, mumble.

mutter (noun)	mussitate (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

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