The Collaborative International Dictionary of English v.0.48:

Debacle \De*ba"cle\, n. [F. d['e]b[^a]cle, fr. d['e]b[^a]cler to
   unbar, break loose; pref. d['e]- (prob. = L. dis) + b[^a]cler
   to bolt, fr. L. baculum a stick.]
   1. (Geol.) A breaking or bursting forth; a violent rush or
      flood of waters which breaks down opposing barriers, and
      hurls forward and disperses blocks of stone and other
      d['e]bris.
      [1913 Webster]

   2. A sudden breaking up or breaking loose; a violent
      dispersion or disruption; impetuous rush; outburst.
      [Webster 1913 Suppl.]

   3. a complete and ludicrous failure; a rout, as of an army; a
      great disaster; a fiasco.
      [PJC]

WordNet (r) 3.0 (2006):

debacle
    n 1: a sudden and violent collapse [syn: debacle, fiasco]
    2: flooding caused by a tumultuous breakup of ice in a river
       during the spring or summer
    3: a sound defeat [syn: thrashing, walloping, debacle,
       drubbing, slaughter, trouncing, whipping]

Moby Thesaurus II by Grady Ward, 1.0:

106 Moby Thesaurus words for "debacle":
   Waterloo, beating, bloodless revolution, bouleversement, breakdown,
   breaking up, breakup, cascade, cataclysm, cataract, catastrophe,
   cave, cave-in, chute, clean slate, clean sweep, collapse, comedown,
   computer revolution, conquering, conquest, convulsion,
   counterrevolution, crack-up, crash, deathblow, declension,
   declination, defeasance, defeat, defluxion, descending, descension,
   descent, destruction, disaster, down, downbend, downcome,
   downcurve, downfall, downflow, downgrade, downpour, downrush,
   downtrend, downturn, downward trend, drop, dropping, drubbing,
   failure, fall, falling, gravitation, hiding, inclination,
   lambasting, lathering, licking, mastery, overcoming, overthrow,
   overturn, palace revolution, plummeting, pounce, quietus,
   radical change, rapids, revolt, revolution, revolutionary war,
   revulsion, rout, ruin, shellacking, shipwreck, smash, smashup,
   spasm, stoop, striking alteration, subdual, subduing, subjugation,
   subversion, sweeping change, swoop, tabula rasa,
   technological revolution, thrashing, total change, total loss,
   transilience, trimming, trouncing, undoing, upset, vanquishment,
   violent change, washout, waterfall, whipping, wrack, wreck