1. [n]  a complaint uttered in a low and indistinct tone
2. [n]  a low continuous indistinct sound; often accompanied by movement of the lips without the production of articulate speech
3. [v]  complain quietly
4. [v]  talk indistinctly; usually in a low voice

1. \Mut"ter\, v. i. [imp. & p. p. {Muttered}; p. pr. & vb.
   n. {Muttering}.] [Prob. of imitative origin; cf. L. muttire,
   mutire.]
   1. To utter words indistinctly or with a low voice and lips
      partly closed; esp., to utter indistinct complaints or
      angry expressions; to grumble; to growl.
   
            Wizards that peep, and that mutter.   --Is. viii.
                                                  19.
   
            Meantime your filthy foreigner will stare, And
            mutter to himself.                    --Dryden.
   
   2. To sound with a low, rumbling noise.
   
            Thick lightnings flash, the muttering thunder rolls.
                                                  --Pope.
   
   

2. \Mut"ter\, v. t.
   To utter with imperfect articulations, or with a low voice;
   as, to mutter threats. --Shak.
   
   

3. \Mut"ter\, n.
   Repressed or obscure utterance.
   
   

To quietly enter a command not meant for the ears, eyes, or fingers of ordinary mortals. Often used in "mutter an incantation".

See also wizard.

[jargon file]