What term did Tolkien use for a sudden turn from despair to joy in a fairy-story?

Tolkien used the term eucatastrophe for a sudden turn from despair to joy in a fairy-story.

He discussed the idea in his 1939 lecture and 1947 essay “On Fairy-Stories.” Tolkien formed the word from Greek elements meaning “good” and “downfall” or “disaster.” For him, a eucatastrophe was not merely a happy ending; it was a sudden, credible reversal that produces profound joy after apparent defeat.

Tolkien considered this turn central to the emotional power of fairy-stories. He also connected it with what he called the “eucatastrophic” shape of the Christian story, while distinguishing literary hope from simple escapism. In his fiction, the concept appears in moments such as the rescue of the quest at the Cracks of Doom.

The term is often confused with subcreation, Tolkien’s idea of imaginative world-building, and mythopoeia, the making of myths. Those concepts are related to his literary theory but do not specifically name the sudden joyful reversal.