grumbler

intransitive verb grumbled, grumbling

1. to make low, unintelligible sounds in the throat; growl
2. to mutter or mumble in discontent; complain in a surly or peevish manner
3. to rumble, as thunder

Origin: prob. < Du grommelen, akin to Ger grummeln, OE gremman, to enrage: for IE base see grim

transitive verb

noun

1. the act of grumbling, esp. in complaint
2. a rumble