Mut·ter v. i. [imp. & p. p. Muttered p. pr. & vb. n. Muttering.]
 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.