Back biter (5)
I believe the answer is:
molar
'back biter' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for molar that I've seen before include "part of the daily grind" , "Chewer and grinder" , "Grinding tooth in the back of a mammal's mouth" , "Type of tooth" , "Broad-crowned tooth" .)