Not all look in a waterway for a coral island (7)
I believe the answer is:
okinawa
'a coral island' is the definition.
(I've seen this before)
'not all look in a waterway' is the wordplay.
'not all' says the answer is hidden in the clue (only some of the letters).
'OKINAWA' is hidden within 'look in a waterway'.
'for' acts as a link.
(Other definitions for okinawa that I've seen before include "Group of small islands in southern Japan with US military presence" , "Region of southern Japan, scene of fierce fighting in 1945" , "Japanese island, capital Naha" , "battle!" , "Japanese location" .)