Mutter :: 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 :: Mutter (v. i.) To sound with a low, rumbling noise..
Mutter :: Mutter (v. t.) To utter with imperfect articulations, or with a low voice; as, to mutter threats..
Mutter :: Mutter (n.) Repressed or obscure utterance.