It’s a fun little word coined by Tolkien that basically means “I know we all assume the worst possible thing can happen, except every now and then, the best possible thing can happen.” A good example would be from a Tolkien-work itself which is the eagles showing up to save Frodo at the end. Damn, that was lucky.

It’s also interesting to contrast the concept of eucatastrophe with the concept of serendipity. They both sort of mean “good luck.” So is there a difference?

Actually, yes.

The difference is in levels of magnitude. Serendipity is just a moment of good luck. “Found five bucks on the street, that was serendipitous.” You’d never call it eucatastrofus (but let’s be honest, no one has called anything “eucatastrofus”). The difference lies in the insane level of luck required to qualify as eucatastrophe. Finding five bucks on the street doesn’t count. The eagles showing up at the end to save your life does.