"the faculty or phenomenon of finding valuable or agreeable things not sought for."
The word was first used in 1754 by writer and parliament member Horace Walpole. In a letter to a friend, Walpole wrote that he came up with "serendipity" while remembering a once read fairy tale, "The Three Princes of Serendip".
While traveling from their small island nation off the southern tip of India, the princes frequently made discoveries of things not intentionally sought after.
Many marvels from the benefits of penicillin to the wonders of Viagra:) have been discovered while researching for entirely different purpose.
So, what better way to describe that chance meeting that results in that amazing relationship? How often do we ask ourselves those hundreds of "what if" questions referring to the slight change of plans, timing, or choices that would have resulted in never meeting our special someone?
A UK translation site lists serendipity as one of the most difficult words to translate in the English language.
The word itself may break down in translation, but the true meaning is universal.
http://writersalmanac.publicradio.org/index.php?date=2010/01/28
