Source : Webster's Revised Unabridged Dictionary (1913)

Gnawer \Gnaw"er\, n.
   1. One who, or that which, gnaws.

   2. (Zo["o]l.) A rodent.

Source : WordNet®

gnawer
     n : relatively small gnawing animals having a single pair of
         constantly growing incisor teeth specialized for gnawing
         [syn: {rodent}, {gnawing animal}]