Synonyms of 'mumble'
murmurDictionary, whisper, whisperingShe could hear the low mumble of his voice.
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If you say something in an undertone, you say it very quietly.
Well-dressed clients were talking in polite undertones as they ate.
When you whisper, you say something very quietly, using your breath rather than your throat, so that only one person can hear you.
‘Keep your voice down,’ I whispered.
Thesaurus for mumble from the Collins English Thesaurus
If you mumble , you speak very quietly and not at all clearly with the result that the words are difficult to understand .