Polecat kin (6)
I believe the answer is:
'polecat kin' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for ferret that I've seen before include "Diligent searcher" , "Assiduous searcher" , "Animal to hunt rats and rabbits" , "Small fierce animal - good hunting rabbits" , "Search about persistently" .)