in architecture, an arch or branch of a Gothic vault; which, instead of being circular, passes diagonally from one angle to another, and forms a crois with the other arches. The middle, where the ogives cross each other, is called the key; being cut in form of a rose, or a cul de lampe. The members or mouldings of the ogives are called nerves, branches, or reins; and the arches which separate the ogives, double arches.