Mink cousin (5)
I believe the answer is:
otter
'mink cousin' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for otter that I've seen before include "Aquatic carnivore" , "Web-footed mammal" , "Good swimmer" , "River-dwelling mammal" , "Mammal, 'Tarka'" .)