Island produce (3)
I believe the answer is:
cos
I believe this clue is a double definition.
'island' is the first definition.
(Greek island)
'produce' is the second definition.
(cos is a kind of produce)
(Other definitions for cos that I've seen before include "in the Dodecanese?" , "Casual as" , "Greek island and type of lettuce" , "Mozart fidelity-test opera" , "often associated with sin" .)