1 a great and usu. sudden disaster.
2 the denouement of a drama.
3 a disastrous end; ruin.
4 an event producing a subversion of the order of things.
Derivatives:
catastrophic adj. catastrophically adv.
Etymology: L catastropha f. Gk katastrophe (as CATA-, strophe turning f. strepho turn)
Useful english dictionary. 2012.