big one

Meanings

1. Something important; (with 'the') the most important one, (especially sports) the big game, the big play.
2. One hundred or one thousand dollars.
3. A dollar.

1. Death.

1. A hypothetical massive earthquake somewhere along the Pacific coast of North America, but especially one projected to cause catastrophic damage to a major city such as Vancouver, Seattle, San Francisco, or Los Angeles.
2. Any other hypothetical event with the potential to be far more devastating than previous events of the same type.