Curtailed rascal’s swindle (4)
I believe the answer is:
scam
'swindle' is the definition.
(scam is a kind of swindle)
'curtailed rascal's' is the wordplay.
'curtailed' means to remove the last letter.
'rascal' becomes 'scamp' ('scamp' can be a synonym of 'rascal').
'scamp' with its last letter taken off is 'SCAM'.
(Other definitions for scam that I've seen before include "ploy" , "Hoax" , "Swindle (Slang)" , "Rip-off" , "Fraudulent business scheme" .)