Solid fuel, fine stored in church (4)
I believe the answer is:
coke
'solid fuel' is the definition.
(type of fuel made from coal)
'fine stored in church' is the wordplay.
'fine' becomes 'ok' (synonyms).
'stored in' indicates putting letters inside.
'church' becomes 'ce' (abbreviation for Church of England).
'ok' placed within 'ce' is 'COKE'.
(Other definitions for coke that I've seen before include "something for heating" , "Residue from coal used as fuel" , "Carbonised fuel residue" , "Drug (abbr) - soft drink (abbr)" , "Solid fuel - drink - drug" .)