Flippancy (6)
I believe the answer is:
levity
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">flippancy</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 levity that I've seen before include "Hair-piece" , "Disrespectful humour" , "Frivolous tendency" , "Manner lacking seriousness" , "thoughtlessness" .)