Source of jelly part filling stomach after exercises (9)
I believe the answer is:
petroleum
'source of jelly' is the definition.
(as in petroleum jelly)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for petroleum that I've seen before include "Hydrocarbon fuel" , "It helps in getting things moving" , "Fossil fuel" , "Fuel oil" , "Oil well product" .)