adverb (r)

• in a serious manner(adv.all)

  Example:
  The speech was weighty and it was weightily delivered.
  

  Synonym:
  earnestly, in earnest, seriously
  

  source: wordnet30
• as something very heavy(adv.all)

  Example:
  She moved weightily.
  

  source: wordnet30
• In a weighty manner.(adverb)

  source: webster1913