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]

Moby Thesaurus II by Grady Ward, 1.0:

171 Moby Thesaurus words for "catastrophe":
   Z, accident, action, anagnorisis, angle, apodosis, architectonics,
   architecture, argument, atmosphere, background, bad luck,
   bitter end, bloodless revolution, blow, bouleversement, breakdown,
   breaking up, breakup, calamity, casualty, cataclysm, cave, cave-in,
   ceasing, cessation, characterization, clean slate, clean sweep,
   climax, coda, collapse, collision, color, completion, complication,
   computer revolution, conclusion, consummation, continuity,
   contretemps, contrivance, convulsion, counterrevolution,
   crack of doom, crack-up, crash, culmination, curtain, curtains,
   death, debacle, decease, denouement, design, destination, destiny,
   development, device, disaster, doom, effect, end, end point,
   end result, ending, envoi, epilogue, episode, eschatology,
   expiration, fable, failure, falling action, fate, fiasco,
   final result, final solution, final twitch, final words, finale,
   finality, finis, finish, gimmick, goal, grief, ill hap, incident,
   izzard, last, last act, last breath, last gasp, last things,
   last trumpet, last words, latter end, line, local color,
   misadventure, mischance, misfortune, mishap, mood, motif, movement,
   mythos, nasty blow, omega, overthrow, overturn, palace revolution,
   payoff, period, peripeteia, peroration, pileup, plan, plot,
   quietus, radical change, recognition, resolution, resting place,
   revolt, revolution, revolutionary war, revulsion, rising action,
   scheme, secondary plot, shipwreck, shock, slant, smash, smashup,
   spasm, staggering blow, stoppage, stopping place, story,
   striking alteration, structure, subject, subplot, subversion,
   swan song, sweeping change, switch, tabula rasa,
   technological revolution, term, terminal, termination, terminus,
   thematic development, theme, tone, topic, total change, total loss,
   tragedy, transilience, twist, upset, violent change, washout,
   windup, wrack, wreck