v.1. To bite or chew something a bit at a time: The fox gnawed the tough meat away first, and then bit into the bone.
2. To bite or chew on something repeatedly in order to grind it down or to remove small pieces from it a bit at a time: The kids gnawed away at the cobs of fresh corn. That dog will gnaw away at that bone until it gets to the marrow inside.
3. To cause someone or something to have or feel persistent discomfort, anxiety, or guilt: Dark thoughts gnawed away at my mind.