collapsev. i.[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.()n.1. A falling together suddenly, as of the sides of a hollow vessel.()2. A sudden and complete failure; an utter failure of any kind; a breakdown.()3. (Med.) Extreme depression or sudden failing of all the vital powers, as the result of disease, injury, or nervous disturbance.()