Monkey business (8)
I believe the answer is:
mischief
'monkey business' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for mischief that I've seen before include "Playful troublemaking" , "Devilment, roguishness" , "injury" , "Naughtiness, trouble" , "Devilment, impishness" .)