noun

1. the culminating event of a drama, esp. of a tragedy, by which the plot is resolved; denouement
2. a disastrous end, bringing overthrow or ruin
3. any great and sudden calamity, disaster, or misfortune
4. a total or ignominious failure
5. Geol. a sudden, violent change, such as an earthquake

Etymology: L catastropha < Gr katastrophē, an overthrowing < katastrephein, to overturn < kata-, down + strephein, to turn: see strophe