- Grumble - Mumble - Speak quietly - 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. - To sound with a low, rumbling noise. - To utter with imperfect articulations, or with a low
voice; as, to mutter threats. - Repressed or obscure utterance.