adverb (r)

• in a joyous manner(adv.all)

  Example:
  They shouted happily.
  

  Synonym:
  blithely, gayly, jubilantly, merrily, mirthfully
  Antonym:
  unhappily
  

  source: wordnet30
• in an unexpectedly lucky way(adv.all)

  Example:
  Happily he was not injured.
  

  Antonym:
  sadly, unhappily
  

  source: wordnet30
• By chance; peradventure; haply.(adverb)

  source: webster1913