Burn fish (4)
I believe the answer is:
char
This clue is a double definition.
'burn' is the first definition.
(charring is a kind of burning)
'fish' is the second definition.
(char is a kind of fish)
(Other definitions for char that I've seen before include "Singe, scorch" , "Sear - fish" , "Scorch: trout-like fish" , "'Mrs Mopp'" , "Fish < tea" .)