Light-heartedness (6)
I believe the answer is:
levity
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">light-heartedness</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 "Light-heartedness" , "Manner lacking seriousness" , "Light quality" , "Hair-piece" , "Frivolity, lightweight laughter" .)