n. In arch.:n. Any one of the ribs of a groined vault, but especially that part of a rib which forms one of the sides of a compartment of the groiningn. A projecting molding, particularly if small and acute-angled in profile. Also called nerve.n. In botany, a vein or nerve of a leaf.n. In entomology, one of the tubes or tubular thickenings which ramify in an insect's wing: a nerve, vein, or costa proceeding along one of certain definite lines, to strengthen the wing and, through a central hollow, to nourish it.