Overcook fish (4)
I believe the answer is:
char
I believe this is a double definition.
'overcook' is the first definition.
(I've seen this in another clue)
'fish' is the second definition.
(char is a kind of fish)
(Other definitions for char that I've seen before include "Make black by burning, or a small trout" , "Domestic employee" , "Singe; a fish" , "Burn slightly" , "Burn lightly" .)