Gnaw

To bite, as something hard or tough, which is not readily separated or crushed; to bite off little by little, with effort; to wear or eat away by scraping or continuous biting with the teeth; to nibble at.

To bite in agony or rage.

To corrode; to fret away; to waste.

To use the teeth in biting; to bite with repeated effort, as in eating or removing with the teethsomething hard, unwiedly, or unmanageable.