Animal at home in a sett (6)
I believe the answer is:
badger
'animal at home in a sett' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for badger that I've seen before include "nocturnal creature" , "Pester - nocturnal animal" , "Grab Ed from the animal" , "Countryside mammal" , "Torment" .)