Not seriously (2,3)
I believe the answer is:
in fun
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">not seriously</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for in fun that I've seen before include "Not intended seriously" , "to raise a smile?" , "As a joke - not seriously" , "for a laugh" .)