Winter stoat (6)
I believe the answer is:
ermine
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">winter stoat</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 ermine that I've seen before include "Animal with brown fur that turns white in winter" , "garb for nobility" , "Fur-bearing mammal" , "Winter fur of the stoat" , "White fur of stoat" .)