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"