Edible flatfish (5,4)
'edible flatfish' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for lemon sole that I've seen before include "fish to eat" , "Tasty plaice of citrus origin?" , "Another tasty flatfish like lone citrus fruit" , "Edible flatfish" , "Flatfish, valued as food" .)
(Other definitions for dover sole that I've seen before include "Kentish flat fish" , "Catch" .)