grumble (v.) Look up grumble at Dictionary.com
1580s, from Middle French grommeler "mutter between the teeth" or directly from Middle Dutch grommelen "murmur, mutter, grunt," from grommen "to rumble, growl." Imitative, or perhaps akin to grim. Related: Grumbled; grumbling.
grumble (n.) Look up grumble at Dictionary.com
1620s, from grumble (v.).