Mischievous child, not complete fraud (4)
I believe the answer is:
scam
'fraud' is the definition.
(scam is a kind of fraud)
'mischievous child not complete' is the wordplay.
'mischievous child' becomes 'scamp' (I've seen this before).
'not complete' means to remove the last letter.
'scamp' with its last letter removed is 'SCAM'.
(Other definitions for scam that I've seen before include "Hoax" , "Fraudulent trick or swindle" , "An informal swindle" , "Fraud, dishonest scheme" , "Rip off" .)