Source : Webster's Revised Unabridged Dictionary (1913)

Mumbling \Mum"bling\, a.
   Low; indistinct; inarticulate. -- {Mum"bling*ly}, adv.

Mumble \Mum"ble\, v. t. [imp. & p. p. {Mumbled}; p. pr. & vb. n.
   {Mumbling}.] [OE. momelen; cf. D. mompelen, mommelen, G.
   mummelen, Sw. mumla, Dan. mumle. Cf. {Mum}, a., {Mumm},
   {Mump}, v.]
   1. 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.

            Peace, you mumbling fool.             --Shak.

            A wrinkled hag, with age grown double, Picking dry
            sticks, and mumbling to herself.      --Otway.

   2. To chew something gently with closed lips.

Source : WordNet®

mumbling
     adj : speaking low and indistinctly; "a mumbling parson stood
           beside the dying man"; "muttering crowds of onlookers"
           [syn: {muttering}]
     n 1: indistinct enunciation
     2: ineffectual chewing (as if without teeth) [syn: {gumming}]