Gk. eu – good; cata – down, back, against; strophe – a twisting, or turning; catastrophe, “an overturning.”
As opposed to the regular catastrophes, a eucatastrophe is “the sudden happy turn in a story which pierces you with joy and brings tears.” An unexpected, happy ending.
Related: serendipity; deus ex machina, peripeteia.
This neologism was invented by J.R.R. Tolkein.