Nocturnal marsupial (7)
I believe the answer is:
opossum
'nocturnal marsupial' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for opossum that I've seen before include "Thick-furred marsupial of the Americas" , "Small Australian marsupial" , "American arboreal marsupial" , "American animal" , "Large marsupial" .)