One of my favorite words of all time!
Evidently invented by Horace Walpole, known for his neo-Gothic architectural eccentricities and author of The Castle of Otranto, in a letter he wrote in 1754. He adapted it from the Italian translation of a Sri Lankan tale (translated from Persian) called the Three Princes of Serendip, a story Walpole read and in which the heroes were always accidentally making discoveries. Sri Lankan from Arabic from Tamil from Sanskrit Whew! The tale is adapted by Voltaire in Zadig.
What is most fascinating about this etymological extravaganza is that serendipity is evidently one of the most impossible of English words to translate.
The method of serendipitous discovery is fundamental, of course, to the beginnings of detective novels –