Gnaw (verb)

1. To bite or chew on persistently (as a rodent gnaws on a piece of wood).
2. To wear away gradually (as a constant worry gnaws at one's peace of mind).

Origin:

Middle english gnawen, from old english gnagan; akin to old high german gnagan to gnaw.

Examples:

1. The mouse gnawed a hole in the wall.
2. The constant worry gnawed at her peace of mind.
3. The dog gnawed on the bone for hours.
4. The constant pain gnawed at his back.
5. The hunger gnawed at his stomach.