Economy that contains false notion (4)
I believe the answer is:
myth
'false notion' is the definition.
(I've seen this before)
'economy that contains' is the wordplay.
'contains' says the answer is hidden in the clue.
'MYTH' is hidden in the letters of 'economy that'.
(Other definitions for myth that I've seen before include "Tall tale" , "false interpretation?" , "Story of old gods" , "lie!" , "Common false belief" .)