Shady scheme (4)
I believe the answer is:
scam
'shady scheme' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for scam that I've seen before include "Swindle (Slang)" , "Hoax" , "ploy" , "Fraudulent action" , "Fraud, trick (slang)" .)