grumble

from The American Heritage® Dictionary of the English Language, 5th Edition.

• intransitive verb To complain in a surly manner; mutter discontentedly.
• intransitive verb To rumble or growl.
• intransitive verb To express in a grumbling discontented manner.
• noun A muttered complaint.
• noun A rumble; a growl.

from The Century Dictionary.

• To make a low rumbling sound; mutter; growl.
• To complain in a low, surly voice; murmur with discontent.
• Synonyms To complain, repine, croak.
• To express or utter in a grumbling or complaining manner.
• noun The act of grumbling; a grumbling speech or remark.
• noun A surly person.
• noun plural A grumbling, discontented mood; a fit of the spleen.

from the GNU version of the Collaborative International Dictionary of English.

• noun The noise of one that grumbles.
• noun A grumbling, discontented disposition.
• intransitive verb To murmur or mutter with discontent; to make ill-natured complaints in a low voice and a surly manner.
• intransitive verb To growl; to snarl in deep tones.
• intransitive verb To rumble; to make a low, harsh, and heavy sound; to mutter.
• transitive verb To express or utter with grumbling.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun onomatopoeia A low thundering, rumbling or growling sound
• noun The sound made by a hungry stomach
• noun A complaint
• verb intransitive To make a low, growling or rumbling noise, like a hungry stomach or certain animals.
• verb intransitive To complain.
• verb transitive To utter in a grumbling fashion.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• verb make complaining remarks or noises under one's breath
• noun a complaint uttered in a low and indistinct tone
• noun a loud low dull continuous noise
• verb make a low noise
• verb to utter or emit low dull rumbling sounds
• verb show one's unhappiness or critical attitude