Polecat; diligent investigator (6)

I believe the answer is:

ferret

(Other definitions for ferret that I've seen before include "Rabbit-unearthing animal" , "Animal bred for hunting rats and rabbits" , "European polecat bred for hunting rabbits" , "Small animal used to drive rabbits from burrows" , "Tame polecat" .)

I've seen this clue in the Sydney Morning Herald.

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