Expressing mirth (8)
I believe the answer is:
laughing
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">expressing mirth</span>' is the definition.<br/ ><span class="explanation-format__explanation">('laugh' can be a synonym of 'express mirth')</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for laughing that I've seen before include "Kookaburra" , "Reacting to comedy" , "Expressing mirth" , "Expressing loud amusement" , "Showing mirth" .)