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