Synonyms of 'mumble'
murmurDictionary, whisper, whispering
She could hear the low mumble of his voice.
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If you murmur something, you say it very quietly, so that not many people can hear what you are saying.
He turned and murmured something to the professor.
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 .