adverb (r)

• deeply or completely(adv.all)

  Example:
  Slept soundly through the storm.
  The baby is sleeping soundly.
  

  source: wordnet30
• completely and absolutely (`good' is sometimes used informally for `thoroughly')(adv.all)

  Example:
  He was soundly defeated.
  

  Synonym:
  good, thoroughly
  

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

  source: webster1913