What term did J.R.R. Tolkien use for a sudden joyful deliverance in a story?

J.R.R. Tolkien used the term eucatastrophe for a sudden joyful turn that brings deliverance in a story.

He introduced the word in his 1947 essay “On Fairy-Stories.” Tolkien formed it from Greek roots, combining eu-, meaning “good,” with catastrophe, a decisive reversal or disastrous turn. For him, eucatastrophe was not merely a convenient happy ending; it was a sudden change from apparently unavoidable ruin into joy.

Tolkien connected the idea with the emotional power he believed fairy-stories could achieve. He also described the Christian story of the Resurrection as the greatest eucatastrophe, while distinguishing that theological claim from ordinary fictional plots. The term is often confused with deus ex machina, but the concepts are not identical. A deus ex machina is an externally imposed solution, whereas eucatastrophe describes the shape and emotional effect of a fortunate reversal. Tolkien’s term is now used in literary criticism beyond discussion of Middle-earth.