n. 1. (Engin.) A vertical pipe, open at the top, between a hydrant and a reservoir, to equalize the flow of water; also, a large vertical pipe, near a pumping engine, into which water is forced up, so as to give it sufficient head to rise to the required level at a distance. [ 1913 Webster ]

2. (Steam Boiler) A supply pipe of sufficient elevation to enable the water to flow into the boiler, notwithstanding the pressure of the steam. Knight. [ 1913 Webster ]