Express mirth (5)
I believe the answer is:
laugh
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">express mirth</span>' is the definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for laugh that I've seen before include "Fun person" , "Chuckle" , "Audible expression of amusement" , "Chortle" , "a ridiculous thing" .)