Bemused with creature (3)
I believe the answer is:
emu
'creature' is the definition.
(emu is a kind of creature)
'bemused with' is the wordplay.
'with' indicates a hidden word.
'EMU' is hidden within 'bemused'.
(Other definitions for emu that I've seen before include "Australian running bird." , "Aussie runner" , "unit of measurement" , "Australian non-flyer" , "Parky's nemesis" .)