|Noah Webster's Dictionary|
1. (v.) To speak with the lips partly closed, so as to render the sounds inarticulate and imperfect; to utter words in a grumbling indistinct manner, indicating discontent or displeasure; to mutter.
2. (v.) To chew something gently with closed lips.
3. (v. t.) To utter with a low, inarticulate voice.
4. (v. t.) To chew or bite gently, as one without teeth.
5. (v. t.) To suppress, or utter imperfectly.
Mumble (1 Occurrence)
Isaiah 29:4 You will be brought down, and will speak out of the ground. Your speech will mumble out of the dust. Your voice will be as of one who has a familiar spirit, out of the ground, and your speech will whisper out of the dust. (WEB NIV)