noun (n)

• an abatement in intensity or degree (as in the manifestations of a disease)(noun.event)

  Synonym:
  remission, remittal
  

  source: wordnet30
• a gradual sinking to a lower level(noun.event)

  Synonym:
  settling, subsiding
  

  source: wordnet30
• the sudden collapse of something into a hollow beneath it(noun.event)

  Synonym:
  cave in
  

  source: wordnet30
• The act or process of subsiding.(noun)

  source: webster1913