SERENDIPITY (from the Oxford English Dictionary)

f. Serendip, a former name for Sri Lanka + -ity. A word coined by Horace Walpole, who says (Let. to Mann, 28 Jan. 1754) that he had formed it upon the title of the fairy-tale `The Three Princes of Serendip', the heroes of which `were always making discoveries, by accidents and sagacity, of things they were not in quest of'.

The faculty of making happy and unexpected discoveries by accident. Also, the fact or an instance of such a discovery.