Source : Webster's Revised Unabridged Dictionary (1913)

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.

            A balloon collapses when the gas escapes from it.
                                                  --Maunder.

   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.

Source : WordNet®

collapsed
     adj : folded compactly; "put the collapsed top hat into its box"