A familiar little marsupial (3)

I believe the answer is:

roo

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'marsupial' is the definition.
(short for kangaroo)

I can't explain the rest of the clue.

(Other definitions for roo that I've seen before include "Young marsupial" , "Small inhabitant of Hundred Acre Wood" , "Kanga's child (Milne)" , "Jumping marsupial" , "Kanga's baby (Pooh)" .)

I've seen this clue in the Evening Standard.

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