Island able to turn (4)
'island' is the definition.
(I've seen this before)
'able to turn' is the wordplay.
'to turn' is a reversal indicator.
'able' reversed gives 'ELBA'.
(Other definitions for elba that I've seen before include "Bale out of the Mediterranean island", "Island of Napoleon's exile in 1814-15", "Italian isle", "Napoleon's plaint: 'Able was I ere I saw . . . .'", "Napoleonic island".)