Jed Clampett's discovery
I believe the answer is:
oil
'jed clampett's discovery' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for oil that I've seen before include "Fluid lubricant" , "Liquid fuel" , "valuable commodity" , "Lubricate; fuel" , "Lubricant or petroleum" .)