Source : Webster's Revised Unabridged Dictionary (1913)

Merrily \Mer"ri*ly\, adv. [From {Merry}.]
   In a merry manner; with mirth; with gayety and laughter;
   jovially. See {Mirth}, and {Merry}.

         Merrily sing, and sport, and play.       --Granville.

Source : WordNet®

merrily
     adv : in a joyous manner; "they shouted happily" [syn: {happily},
           {mirthfully}, {gayly}, {blithely}, {jubilantly}, {with
           happiness}] [ant: {unhappily}]