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.