Fuel from a bog (4)
I believe the answer is:
'fuel from a bog' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for peat that I've seen before include "Natural solid fuel" , "Vegetable matter in bogs, like turf" , "Organic fuel" , "Fuel from bogs" , "Turf as in bogland" .)