Polecat (6)
I believe the answer is:
ferret
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">polecat</span>' is the definition.<br/ ><span class="explanation-format__explanation">(ferret is a kind of polecat)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for ferret that I've seen before include "Animal used to catch rabbits" , "Animal trained to catch rabbits" , "Polecat bred for hunting rats and rabbits" , "Small fierce animal used to hunt rabbits" , "Assiduous searcher" .)