happily vs merrily

happily and merrily both are adverbs.

Word	Noun	Adjective	Verb	Adverb
happily	No	No	No	Yes
merrily	No	No	No	Yes

As adverbs, happily and merrily are synonyms defined as:

Other synonyms of happily include blithely, gayly, jubilantly, mirthfully.

happily (adverb)	merrily (adverb)
in an unexpectedly lucky way	in a joyous manner
in a joyous manner