Merrily (5)
I believe the answer is:
gaily
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">merrily</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 gaily that I've seen before include "Light-heartedly" , "Cheerily, brightly" , "In merry or light-hearted manner" , "Merrily" .)