Monkey business (8)
I believe the answer is:
mischief
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">monkey business</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for mischief that I've seen before include "Playful troublemaking" , "Devilment, roguishness" , "injury" , "Naughtiness, trouble" , "Devilment, impishness" .)