Merrily :: Merrily (adv.) In a merry manner; with mirth; with gayety and laughter; jovially. See Mirth, and Merry..
Merriment :: Merriment (n.) Gayety, with laughter; mirth; frolic..
Merriness :: Merriness (n.) The quality or state of being merry; merriment; mirth; gayety, with laughter..