Hidden bomb (5,4)
I believe the answer is:
booby trap
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">hidden bomb</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for booby trap that I've seen before include "Lethal or playful device set off by victim" , "Device for practical joke" , "hidden hazard" , "hidden bomb, perhaps" , "Hazard for the unwary" .)