The fur of the beaver (6)
I believe the answer is:
castor
'the fur of the beaver' is the definition.
(I've seen this before)
This is all the clue.
(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" .)