either of two large veins discharging blood into the right atrium of the heart, one (superior vena cava or precava) conveying blood from the head, chest, and upper extremities and the other (inferior vena cava or postcava) conveying blood from all parts below the diaphragm.
any of the locations in a jet of fluid emerging from an orifice where the cross section of the jet is at a minimum, especially the location of minimum cross section nearest the orifice.
