Fuel company kept half hidden (4)
I believe the answer is:
coke
'fuel' is the definition.
(I know that coke is a type of fuel)
'company kept half hidden' is the wordplay.
I cannot really see how this works, but
'company' could be 'co' (abbreviation) and 'co' is found within the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for coke that I've seen before include "Substance left after gas and tar have been extracted from coal" , "Residue from coal used as fuel" , "Drink - drug - solid-fuel product" , "Nose candy" , "Carbonised fuel residue" .)