Gem of the ocean (5)
I believe the answer is:
pearl
'gem of the ocean' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for pearl that I've seen before include "Off-white colour" , "one regularly in stitches" , "Lustrous structure inside an oyster-shell" , "Paragon" , "Gem from oyster" .)