Kind of nut inspiring a marsupial (5)
I believe the answer is:
koala
'marsupial' is the definition.
(koala is a kind of marsupial)
'kind of nut inspiring a' is the wordplay.
'kind of nut' becomes 'kola' (kola nut is a type of nut).
'inspiring' is an insertion indicator.
'kola' going around 'a' is 'KOALA'.
(Other definitions for koala that I've seen before include "Arboreal marsupial" , "One's usually up a tree" , "leaf-eater" , "Australian animal" , "Australian creature" .)