n. 25B6; verb
a group of men stood muttering : TALK UNDER ONE'S BREATH, murmur, mumble, whisper, speak in an undertone.
back-benchers muttered about the reshuffle : GRUMBLE, complain, grouse, carp, whine; informal moan, gripe, beef, whinge; Brit. informal chunter; N. Amer. informal kvetch.