Edible bivalve (6)
I believe the answer is:
oyster
'edible bivalve' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for oyster that I've seen before include "World as place of opportunity" , "Secretive individual" , "Content of stew" , "Flat shellfish" , "Shade of greyish white" .)