Fit to return to the island (4)
I believe the answer is:
elba
'the island' is the definition.
(I've seen this before)
'fit to return' is the wordplay.
'fit' becomes 'able' ('able' can be similar in meaning to 'fit').
'to return' is a reversal indicator.
'able' written backwards gives 'ELBA'.
'to' is the link.
(Other definitions for elba that I've seen before include "Italian isle" , "Napoleon's first place of exile" , "''Able was I ere I saw . . . .'' (4)" , "Exile isle for Napoleon" , "place for Napoleon" .)