The Collaborative International Dictionary of English v.0.48:

Collapse \Col*lapse"\, v. i. [imp. & p. p. Collapsed; p. pr. &
   vb. n. Collapsing] [L. collapsus, p. p. of collabi to
   collapse; col- + labi to fall, slide. See Lapse.]
   1. To fall together suddenly, as the sides of a hollow
      vessel; to close by falling or shrinking together; to have
      the sides or parts of (a thing) fall in together, or be
      crushed in together; as, a flue in the boiler of a steam
      engine sometimes collapses.
      [1913 Webster]

            A balloon collapses when the gas escapes from it.
                                                  --Maunder.
      [1913 Webster]

   2. To fail suddenly and completely, like something hollow
      when subject to too much pressure; to undergo a collapse;
      as, Maximilian's government collapsed soon after the
      French army left Mexico; many financial projects collapse
      after attaining some success and importance.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Collapse \Col*lapse"\, n.
   1. A falling together suddenly, as of the sides of a hollow
      vessel.
      [1913 Webster]

   2. A sudden and complete failure; an utter failure of any
      kind; a breakdown. [Colloq.]
      [1913 Webster]

   3. (Med.) Extreme depression or sudden failing of all the
      vital powers, as the result of disease, injury, or nervous
      disturbance.
      [1913 Webster]

WordNet (r) 3.0 (2006):

collapse
    n 1: an abrupt failure of function or complete physical
         exhaustion; "the commander's prostration demoralized his
         men" [syn: collapse, prostration]
    2: a natural event caused by something suddenly falling down or
       caving in; "the roof is in danger of collapse"; "the collapse
       of the old star under its own gravity"
    3: the act of throwing yourself down; "he landed on the bed with
       a great flop" [syn: flop, collapse]
    4: a sudden large decline of business or the prices of stocks
       (especially one that causes additional failures) [syn:
       crash, collapse]
    v 1: break down, literally or metaphorically; "The wall
         collapsed"; "The business collapsed"; "The dam broke"; "The
         roof collapsed"; "The wall gave in"; "The roof finally gave
         under the weight of the ice" [syn: collapse, fall in,
         cave in, give, give way, break, founder]
    2: collapse due to fatigue, an illness, or a sudden attack [syn:
       break down, collapse]
    3: fold or close up; "fold up your umbrella"; "collapse the
       music stand"
    4: fall apart; "the building crumbled after the explosion";
       "Negotiations broke down" [syn: crumble, crumple,
       tumble, break down, collapse]
    5: cause to burst; "The ice broke the pipe" [syn: collapse,
       burst]
    6: suffer a nervous breakdown [syn: crack up, crack, crock
       up, break up, collapse]
    7: lose significance, effectiveness, or value; "The school
       system is collapsing"; "The stock market collapsed"

Moby Thesaurus II by Grady Ward, 1.0:

335 Moby Thesaurus words for "collapse":
   OD, Waterloo, amiable weakness, bankruptcy, be brought down,
   be felled, be found wanting, be ruined, be struck down,
   be traumatized, beating, become insolvent, bend, blow,
   bouncing check, break, break down, break out, break up,
   breakability, breakage, breakdown, breaking up, breakup,
   brittleness, burn out, bust, cascade, catabasis, cataclysm,
   cataract, catastrophe, catch, catch cold, cave, cave in, cave-in,
   changeableness, chute, circulatory collapse, collapse, come apart,
   come down, come down with, come short, come to naught,
   come to nothing, come unstuck, comedown, conk out, conquering,
   conquest, contract, crack, crack up, crack-up, crackup, crash,
   crippling, cropper, crumble, crumple, daintiness, damage,
   deathblow, debacle, deceleration, declension, declination, decline,
   decline and fall, decrescendo, defeat, deflate, deflation,
   defluxion, delicacy, descend, descending, descension, descent,
   destructibility, destruction, detriment, dilapidation, diminish,
   diminuendo, dip down, disablement, disappear, disappearance,
   disaster, disintegrate, disintegration, disorganization, disrepair,
   disruption, dissolution, dissolve, dive, down, downbend, downcome,
   downcurve, downfall, downflow, downgrade, downpour, downrush,
   downtrend, downturn, downward trend, draining, droop, drop,
   drop down, drop off, dropping, drubbing, dwindling, ebb,
   effeminacy, encroachment, erupt, evaporate, exhaust, exhaustedness,
   exhaustion, fade, fag, fail, failure, faint, fall, fall away,
   fall dead, fall down, fall flat, fall in, fall off, fall short,
   fall stillborn, fall through, fall to pieces, falling, fatigue,
   fever, fizzle out, flag, flimsiness, fold, fold up, founder,
   fragility, frailty, frangibility, gasp, get, get bogged down,
   get hung up, get mired, get tired, give out, give way, go,
   go bankrupt, go broke, go down, go downhill, go into receivership,
   go into shock, go soft, go to pieces, go to pot, go to ruin,
   go to smash, go under, go up, gravitate, gravitation, grow weary,
   harm, hiding, hit the skids, hobbling, human frailty, hurt,
   hurting, impairment, implode, implosion, incapacitation,
   inclination, indecisiveness, infirmity of will, infringement,
   inherent vice, injury, inroad, insolvency, insufficient funds,
   irresolution, jade, keel over, kited check, lack, lag, lambasting,
   languish, lapse, lathering, licking, lightness, lose altitude,
   lose ground, loss, maiming, mastery, mayhem, mischief,
   moral weakness, mutilation, nervous breakdown, nervous exhaustion,
   nervous prostration, neurasthenia, nose dive, not answer,
   not hack it, not make it, not make out, not measure up,
   not stretch, not suffice, overcoming, overdose, overdraft,
   overdrawn account, overthrow, overturn, pant, parachute, pass out,
   peg out, peter out, pine, pitch, play out, plummet, plummeting,
   plunge, poop out, pounce, pour down, pratfall, precipitate,
   prostration, puff, puff and blow, puncture, quietus, rain, rapids,
   receivership, remission, retreat, ruin, ruination, ruining,
   ruinousness, run a temperature, run down, run out, run short,
   sabotage, scathe, shatter, shipwreck, shut down, sicken, sickening,
   sink, sleaziness, slightness, slowdown, slump, smash, smashup,
   spoiling, stoop, stop short, stumble, subdual, subduing,
   subjugation, subsidence, succumb, sway, swoon, swoop, tailspin,
   take, take ill, thrashing, tire, topple, topple down, topple over,
   total loss, totter, trend downward, trimming, trouncing, tumble,
   undoing, unsubstantiality, vanquishment, velleity, wane, want,
   washout, waterfall, weaken, weakening, wear away, wear thin, weary,
   wheeze, whipping, wilt, wispiness, womanishness, wrack, wreck,
   yield