adverb (r)

• introducing a different topic; in point of fact(adv.all)

  Example:
  Incidentally, I won't go to the party.
  

  source: wordnet30
• of a minor or subordinate nature(adv.all)

  Example:
  These magnificent achievements were only incidentally influenced by Oriental models.
  

  Synonym:
  accidentally
  

  source: wordnet30