To obliterate, replace, make void, or useless.
Supersede means to take the place of, as by reason of superior worth or right. A recently enacted statute that repeals an older law is said to supersede the prior legislation.
A superseding cause is an act of a third person or some intervening force that prevents a tortfeasor from being held liable for harm to another. A supervening act is one that insulates an actor from responsibility for negligently causing a dangerous condition that results in an injury to the plaintiff.