gnaw

verb

1. bite or chew on with the teeth

   verb.contact

   Examples

   Gnaw an old cracker.

   Source: WordNet 3.0

2. become ground down or deteriorate

   verb.change

   Synonyms eat at erode gnaw at wear away

   Source: WordNet 3.0

3. 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.

   verb

   Source: webster1913

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

   verb

   Source: webster1913