Eucalyptus-eating marsupial (5)
I believe the answer is:
koala
'eucalyptus-eating marsupial' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for koala that I've seen before include "Arboreal marsupial" , "Australian tree-climbing marsupial with grey fur and big ears" , "Bear-like Australian marsupial" , "One's usually up a tree" , "Aussie gum-chewer?" .)