1 An event causing great and usually sudden damage or suffering; a disaster.
1.1 Something very unfortunate or unsuccessful.
2 The denouement of a drama, especially a classical tragedy.
Mid 16th century (in the sense ‘denouement’): from Latin catastropha, from Greek katastrophē ‘overturning, sudden turn’, from kata- ‘down’ + strophē ‘turning’ (from strephein ‘to turn’).
A minor catastrophe struck my computer early yesterday, failure to boot. Two days of work with a new disk drive has mitigated the issue, but delayed this word.