Emily Dickinson Lexicon

MUM'BLE, v.i. [G. mummeln; D. momelen, mompelen; Sw. mumla; Dan. mumler. This word seems to be connected with mum, in the sense of closeness of the lips.]

1. To mutter; to speak with the lips or other organs partly closed, so as to render the sounds inarticulate and imperfect; to utter words with a grumbling tone. Peace, you mumbling fool. Shak. A wrinkled hag, with age grown double, / Picking dry sticks and mumbling to herself. Otway.
2. To chew or bite softly; to eat with the lips close. Dryden.