1. Pertaining to a great and general flood of water, a deluge: "The cataclysmic rain showers have altered the physical situations in the country because so many people have lost their homes and their living conditions have been devastated."
2. Figuratively, a political or social upheaval that sweeps away the old order of things: "The cataclysmic terror attacks have caused great changes in the social structures of the country."
3. A reference to sudden and violent upheavals or disasters that cause great changes in people's lives: "The severe flooding of a certain country was one cataclysmic disaster, but then the same territory suffered more cataclysmic sufferings from an extreme drought that destroyed crops and caused starvation for thousands of people."