If people or animals gnaw something or gnaw at it, they bite it repeatedly. Woodlice attack living plants and gnaw at the stems Melanie gnawed a long, painted fingernail. = chew
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
If a feeling or thought gnaws at you, it causes you to keep worrying. Doubts were already gnawing away at the back of his mind Mary Ann's exhilaration gave way to gnawing fear. = nag. to keep biting something hard = chew