Sentence:  "The most random <WSD>serendipity</WSD> brought the two of us together, and now, we are happily married! If I was just 15 seconds slower, I'd have never met her!" - 1754 Horace Walpole, "The Letters of Horace Walpole", vol. 2, Letter 90, To Sir Horace Mann, Arlington Street, Jan. 28, 1754. 
Meaning of the word marked with <WSD> tags:  A combination of events which are not individually beneficial, but occurring together to produce a good or wonderful outcome.