Noah Webster's New International Dictionary of the English Language

1. (v. i.) To murmur or mutter with discontent; to make ill-natured complaints in a low voice and a surly manner.

2. (v. i.) To growl; to snarl in deep tones; as, a lion grumbling over his prey.

3. (v. i.) To rumble; to make a low, harsh, and heavy sound; to mutter; as, the distant thunder grumbles.

4. (v. t.) To express or utter with grumbling.

5. (n.) The noise of one that grumbles.

6. (n.) A grumbling, discontented disposition.