Scam, swindle (3)
I believe the answer is:
con
This clue is a double definition.
'scam' is the first definition.
(both can mean a fraudulent scheme)
'swindle' is the second definition.
(I know that swindle can be written as con)
(Other definitions for con that I've seen before include "Have a reason not to" , "one in pen?" , "Diddle" , "Tory" , "Study - trick" .)