Monkey endlessly makes racket (4)
I believe the answer is:
scam
'racket' is the definition.
(I've seen this before)
'monkey endlessly' is the wordplay.
'monkey' becomes 'scamp' (both can mean a mischievous child).
'endlessly' means to remove the last letter.
'scamp' with its last letter taken away is 'SCAM'.
'makes' acts as a link.
(Other definitions for scam that I've seen before include "Fraud, dishonest scheme" , "Confidence trick, swindle" , "Dodgy business" , "Fraudulent business scheme" , "Dubious operation" .)