adverb (r)

• without previous thought or preparation(adv.all)

  Example:
  She had made these remarks offhandedly.
  

  Synonym:
  offhand, offhanded
  

  source: wordnet30
• in a casually inconsiderate manner(adv.all)

  Example:
  She threw him over offhandedly without even a Dear-John letter.
  

  source: wordnet30