Milne's one was doubly good (5)
I believe the answer is:
tiger
'good' is the definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.
I don't understand how the rest of the clue works.
(Other definitions for tiger that I've seen before include "Large feline of the forests" , "Fierce, determined type" , "___ Woods, golfer" , "Striped feline" , "Striped carnivore" .)