Web-footed mammal (5)
I believe the answer is:
otter
'web-footed mammal' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for otter that I've seen before include "furry animal" , "Fish-eating water animal with brown fur and flat tail" , "Semi-aquatic mammal" , "carnivore is concerned" , "Fur possibly" .)