Mirth, merriment (8)
I believe the answer is:
hilarity
<span class="explanation-format__ClueExplanation">I believe this clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">mirth</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ >'<span class="explanation-format__original">merriment</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(hilarity is a kind of merriment)</span><br/ ><br/ ></span>
(Other definitions for hilarity that I've seen before include "Great merriment" , "Great amusement" , "fun" , "Laughter" , "Gaiety" .)