mumble

American Heritage® Dictionary of the English Language, Fourth Edition

1. v. To utter indistinctly by lowering the voice or partially closing the mouth: mumbled an insincere apology.
2. v. To chew slowly or ineffectively without or as if without teeth.
3. v. To speak words indistinctly, as by lowering the voice or partially closing the mouth.
4. v. To chew food slowly or ineffectively, as if with the gums.
5. n. A low indistinct sound or utterance.

Century Dictionary and Cyclopedia

1. To speak with the vocal organs partly closed, so as to render the sounds inarticulate and imperfect; speak in low tones, hesitatingly, or deprecatingly.
2. To chew or bite softly or with the gums; work food with the gums on account of lack or defectiveness of teeth.
3. To utter in a low inarticulate voice.
4. To chew gently; work (food) by rubbing it with the gums on account of lack of teeth.
5. To cover up or hide, as if by uttering in a mumbling, unintelligible fashion; say over inarticulately: with up.
6. n. A low, indistinct utterance.

Wiktionary

1. v. transitive, intransitive To speak unintelligibly or inaudibly; to fail to articulate.
2. n. A quiet or unintelligible vocalization.
3. n. A low tone of voice.

GNU Webster's 1913

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. To utter with a low, inarticulate voice.
4. v. To chew or bite gently, as one without teeth.
5. v. To suppress, or utter imperfectly.

WordNet 3.0

1. v. talk indistinctly; usually in a low voice
2. v. grind with the gums; chew without teeth and with great difficulty
3. n. a soft indistinct utterance