Boggy stuff (4)
I believe the answer is:
peat
'boggy stuff' 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 "Fuel from boggy land" , "Dried turf" , "Tape (anag.)" , "Partially carbonised vegetable matter used as a fuel when dried" , "Fuel dug from bog" .)