The fur of the beaver (6)
I believe the answer is:
castor
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">the fur of the beaver</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 castor that I've seen before include "for wheel? Yes and no" , "Fur of the beaver" , "Small swivelling wheel on a furniture leg" , "Brother to Pollux" , "Powdered sugar" .)