col·lapse / kəˈlaps/ • v. [intr.] 1. (of a structure) fall down or in; give way. ∎  [tr.] cause (something) to fall in or give way: it feels as if the slightest pressure would collapse it | fig. many people tend to collapse the distinction between the two concepts. ∎  (of a lung or blood vessel) fall inward and become flat and empty. ∎  [tr.] cause (a lung or blood vessel) to do this. ∎  fold or be folded to fit into a small space: [intr.] some cots collapse down to fit into a bag. 2. (of a person) fall down and become unconscious, typically through illness or injury. ∎ inf. sit or lie down as a result of tiredness or prolonged exertion.3. (of an institution or undertaking) fail suddenly and completely: in the face of such resolve his opposition finally collapsed. ∎  (of a price or currency) drop suddenly in value.• n. an instance of a structure falling down or in: the church roof is in danger of collapse. ∎  a sudden failure of an institution or undertaking: the collapse of communism. ∎  a physical or mental breakdown: he suffered a collapse from overwork.ORIGIN: early 17th cent. (as collapsed): from medical Latin collapsus, past participle of collabi, from col- ‘together’ + labi ‘to slip.’

collapse vb. XVIII. Back-formation f. pp. collapsed (XVII), f. L. collāpsus, pp. of collābī, f. COL- + lābī fall; see LAPSE, -ED 1.
So collapse sb. XIX.