Definition of Fortuitous event
An event happening by chance or accident. That which happens by a cause which cannot be resisted. An unforeseen occurrence, not caused by either of the parties, nor such as they could prevent. For purposes of an all risk insurance policy, an event which occurs accidentally, as a lay-person, and not a technician or scientist, would understand that term. It is an event which happens by chance, unexpectedly, or without known cause; one which is undesigned or unplanned. Standard Structural Steel Co. v. Bethlehem Steel Corp., D.C.Conn., 597 F.Supp. 164, 193.
That's the definition of Fortuitous event in Black's Law Dictionary 6th Edition. Courtesy of Cekhukum.com.