fortuitous event

noun | \ fȯr-ˈtü-ə-təs-, -ˈtyü- \ | for·tu·i·tous event

1. : an event of natural or human origin that could not have been reasonably foreseen or expected and is out of the control of the persons concerned (as parties to a contract) : force majeure — called also cas fortuit; see also frustration — compare inevitable accident