Coral island (5)
'coral island' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for atoll that I've seen before include "Coral island with central lagoon" , "Pacific coral island" , "Coral isle" , "Bikini, say" , "Coral circle" .)
'coral island' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Another definition for cay that I've seen is " Island".)