Coal or propane
I believe the answer is:
fuel
I believe this is a double definition.
'coal' is the first definition.
(thesaurus)
'propane' is the second definition.
(thesaurus)
(Other definitions for fuel that I've seen before include "Eg, coal or oil" , "Burned source of energy" , "Combustibles" , "Gas, oil or petrol, for instance" , "Combustible material" .)