Definition of "mutter"

mutter¹

/ˈmʌtə/

noun
plural mutters
1. A repressed or obscure utterance; an instance of muttering.
verb
third-person singular simple present mutters, present participle muttering, simple past and past participle muttered
1. To utter words, especially complaints or angry expressions, indistinctly or with a low voice and lips partly closed; to say under one's breath.
  Quotations
  This set – the set of Rosol's life – was studded with aces and menacing ground-strokes that left Nadal an impotent spectator often muttering to himself and at the umpire regarding a perceived misdemeanour by his opponent.
  2012 June 28, Jamie Jackson, “Wimbledon 2012: Lukas Rosol shocked by miracle win over Rafael Nadal”, in the Guardian‎
2. To speak softly and incoherently, or with imperfect articulations.
  Quotations
  Meantime your filthy foreigner will stare, / And mutter to himself.
  1675, John Dryden, Aureng-zebe: A Tragedy. […], London: […] T[homas] N[ewcomb] for Henry Herringman, […], published 1676, (please specify the page number)
3. To make a sound with a low, rumbling noise.
  Quotations
  Thick lightnings flash, the muttering thunder rolls.
  1715–1720, Homer, [Alexander] Pope, transl., “Book VIII”, in The Iliad of Homer, volumes (please specify |volume=I to VI), London: […] W[illiam] Bowyer, for Bernard Lintott […]

/ˈmʌtə/