Island to which Napoleon was exiled (4)
I believe the answer is:
elba
'island to which napoleon was exiled' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for elba that I've seen before include "Napoleon's prison isle" , "part of Tuscany?" , "Napoleon's first place of exile" , "Island in the Med" , "Where emperor was confined" .)