1.a loud low dull continuous noise;
they heard the rumbling of thunder
2.a complaint uttered in a low and indistinct tone
1.show one's unhappiness or critical attitude;
He scolded about anything that he thought was wrong
2.make complaining remarks or noises under one's breath;
she grumbles when she feels overworked
3.to utter or emit low dull rumbling sounds;
he grumbled a rude response
4.make a low noise;
rumbling thunder