Doomsday (noun)

1. The end of the world; the final judgment; the last day.
2. A catastrophic event or crisis, esp. one that leads to the end of the world.

Origin:

Old english dōm, of germanic origin; related to dutch dag "day" and german tag.

Examples:

1. He believed that the end of the world was near and he was preparing for doomsday.
2. The prophecy foretold that doomsday would arrive in 2012.
3. The nuclear war was seen as a potential doomsday event.
4. The asteroid impact was feared as a potential doomsday scenario.
5. The outbreak of the pandemic was seen as a potential doomsday by many.