Flick knife (11)
I believe the answer is:
switchblade
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">flick knife</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 switchblade that I've seen before include "Flick knife (US)" , "offensive weapon" , "that might be handy in a street fight" .)