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