Lat. Chance; accident; an event; a case; a case contemplated. Casus belli. An occurrence giving rise to or justifying war. Casus foederis. In international law. The case of the treaty. The particular event or situation contemplated by the treaty, or stipulated for, or which comes within its terms. In commercial law. The case or event contemplated by the parties to an individual contract or stipulated for by it, or coming within its terms. Casus fortuitus. An inevitable accident, a chance occurrence, or fortuitous event. A loss happening in spite of all human effort and sagacity. 3 Kent. Comm. 217, 300; Whart. Neg.