The Collaborative International Dictionary of English v.0.48:

Catastrophe \Ca*tas"tro*phe\, n. [L. catastropha, Gr. ?, fr. ?
   to turn up and down, to overturn; kata` down + ? to turn.]
   1. 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.
      [1913 Webster]

            The strange catastrophe of affairs now at London.
                                                  --Bp. Burnet.
      [1913 Webster]

            The most horrible and portentous catastrophe that
            nature ever yet saw.                  --Woodward.
      [1913 Webster]

   2. The final event in a romance or a dramatic piece; a
      denouement, as a death in a tragedy, or a marriage in a
      comedy.
      [1913 Webster]

   3. (Geol.) A violent and widely extended change in the
      surface of the earth, as, an elevation or subsidence of
      some part of it, effected by internal causes. --Whewell.
      [1913 Webster]

WordNet (r) 3.0 (2006):

catastrophe
    n 1: an event resulting in great loss and misfortune; "the whole
         city was affected by the irremediable calamity"; "the
         earthquake was a disaster" [syn: calamity, catastrophe,
         disaster, tragedy, cataclysm]
    2: a state of extreme (usually irremediable) ruin and
       misfortune; "lack of funds has resulted in a catastrophe for
       our school system"; "his policies were a disaster" [syn:
       catastrophe, disaster]
    3: a sudden violent change in the earth's surface [syn:
       catastrophe, cataclysm]