noun (n)

• an event resulting in great loss and misfortune(noun.event)

  Synonym:
  calamity, cataclysm, disaster, tragedy
  

  source: wordnet30
• a state of extreme (usually irremediable) ruin and misfortune(noun.state)

  Example:
  Lack of funds has resulted in a catastrophe for our school system.
  

  Synonym:
  disaster
  

  source: wordnet30
• a sudden violent change in the earth's surface(noun.phenomenon)

  Synonym:
  cataclysm
  

  source: wordnet30
• An event producing a subversion of the order or system of things; a final event, usually of a calamitous or disastrous nature; hence, sudden calamity; great misfortune.(noun)

  source: webster1913