1 chew, nibble, eat, bite, champ:
The marks were made by deer gnawing the bark.
2 erode, eat away, corrode, wear down or away, fret, consume, devour:
The acid continues to gnaw away at the metal till it is gone.
3 fret, irritate, harry, hector, pester, worry, bother, plague, trouble, torment, torture, distress, badger, harass, haunt, nag, vex, gall, nettle, irk, peeve, annoy:
The feeling that something was very wrong continued to gnaw at her.