Rat relative (6)
I believe the answer is:
gerbil
'rat relative' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for gerbil that I've seen before include "Small burrowing rodent" , "Mouse-like desert rodent with long hind legs" , "Burrower with a bushy tail" , "Mouse-like rodent (G not J)" , "Burrowing desert rodent" .)