A favourite outdoor fuel (4)
I believe the answer is:
peat
'fuel' is the definition.
(peat is a kind of fuel)
'a favourite outdoor' is the wordplay.
I cannot quite understand how this works, but
'a' is found in the answer.
'favourite' could be 'pet' (synonyms) and 'pet' is found in the leftover letters.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for peat that I've seen before include "Fuel from boggy land" , "Fuel dug from bog" , "Turf as in bogland" , "Vegetable matter in bogs, like turf" , "Form of fuel" .)