A grouse is a plump little bird. Don’t like birds? You can grouse, or complain, about them. The word grouse means both, but a grouse wouldn’t grouse because birds don’t whine.
The word grouse has been around since the 1500s, referring to a ground-dwelling game bird with feathery feet and legs. It’s a bird, so people hunt it, which is maybe how grouse came to mean “to complain” a few hundred years later. You might grouse about the amount of homework your social studies teacher assigns or about the terrible weather or about the high price of gas. People will grouse about pretty much anything!