The Collaborative International Dictionary of English v.0.48:

Gaily \Gai"ly\, adv. [From Gay.]
   Merrily; showily. See gaily.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Gayly \Gay"ly\, adv. [Also spelled gaily.]
   1. With mirth and frolic; merrily; blithely; gleefully.
      [1913 Webster]

   2. Finely; splendidly; showily; as, ladies gayly dressed; a
      flower gayly blooming. --Pope.
      [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

20 Moby Thesaurus words for "gaily":
   airily, blithely, brightly, brilliantly, cheerfully, cheerily,
   colorfully, flamboyantly, flashily, garishly, gaudily, gleefully,
   happily, insouciantly, jauntily, joyfully, jubilantly, merrily,
   showily, splendidly