Burrowing beast (4)
I believe the answer is:
mole
'burrowing beast' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for mole that I've seen before include "Counterspy" , "Spy, skin spot and furry animal" , "Small congenital skin spot" , "Small burrowing animal" , "sauce" .)