"Bear" that's actually a marsupial (5)
I believe the answer is:
koala
'bear that's actually a marsupial' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for koala that I've seen before include "Tree-hugger" , "Aussie tree-climber" , "leaf-eater" , "Arboreal marsupial" , "small bear" .)