Some psychopath on Shutter Island (6)
I believe the answer is:
honshu
'island' is the definition.
(Honshu is an example)
'some psychopath on shutter' is the wordplay.
'some' indicates a hidden word (some of the parts of the word are used).
'HONSHU' is hidden within 'psychopath on shutter'.
(Other definitions for honshu that I've seen before include "Largest island of mainland Japan" , "The main island of Japan" , "Largest of the Japanese islands" , "Island regarded as the Japanese mainland" , "The largest island unit of Japan" .)