Sea-girt location (6)
(Other definitions for island that I've seen before include "Atoll" , "Corsica, for example" , "Detached landmass" , "Man, say" , "Ireland, Jersey or Iceland, say" .)
(Other definitions for isle that I've seen before include "Small region of land" , "Small bit of land surrounded by water" , "Capri for one" , "Could be Man" , "Piece of land in water" .)