JUS INCOGNITUM. An unknown law. This term is applied by the civilians to obsolete laws, which, as Bacon truly observes, are unjust, for the law to be just must give warning before it strikes. Bac. Aphor. 8, s. 1: Bowy. Mod. Civ. Law, 33. But until it has become obsolete no custom can prevail against it. Vide Obsolete.