Assert and Mutter

verb

• State categorically.
  • synonyms: asseverate, maintain
• To declare or affirm solemnly and formally as true.
  • usage: "Before God I swear I am innocent"
  • synonyms: affirm, verify, avow, aver, swan, swear
• Insist on having one's opinions and rights recognized.
  • usage: "Women should assert themselves more"
  • synonyms: put forward
• Assert to be true.
  • usage: "The letter asserts a free society"
  • synonyms: insist

• (v.t.) To maintain; to defend.
• (v.t.) To maintain or defend, as a cause or a claim, by words or measures; to vindicate a claim or title to; as, to assert our rights and liberties.
• (v.t.) To affirm; to declare with assurance or plainly and strongly; to state positively; to aver; to asseverate.

noun

• A low continuous indistinct sound; often accompanied by movement of the lips without the production of articulate speech.
  • synonyms: muttering, murmur, murmuring, murmuration, mussitation
• A complaint uttered in a low and indistinct tone.
  • synonyms: grumble, grumbling, murmur, murmuring, muttering

verb

• Talk indistinctly; usually in a low voice.
  • synonyms: mumble, maunder, mussitate
• Make complaining remarks or noises under one's breath.
  • usage: "she grumbles when she feels overworked"
  • synonyms: murmur, grumble, croak, gnarl

• (v.i.) To utter words indistinctly or with a low voice and lips partly closed; especially, to utter indistinct complaints or angry expressions; to grumble; to growl.
• (n.) Repressed or obscure utterance.
• (v.i.) To sound with a low, rumbling noise.
• (v.t.) To utter with imperfect articulations or with a low voice; as, to mutter threats.