Chewed (6)
I believe the answer is:
gnawed
'chewed' is the definition.
(gnawing is a kind of chewing)
This is the entire clue.
(Other definitions for gnawed that I've seen before include "Bit persistently at something hard" , "Persistently nibbled" , "Worried persistently" , "Chewed at like dog with bone" , "Bit or chewed persistently" .)