n. A dam in a river to stop and raise the water, for the purpose of conducting it to a mill, forming a fish pond, or the like.n. A fence of stakes, brushwood, or the like, set in a stream, tideway, or inlet of the sea, for taking fish.n. A long notch with a horizontal edge, as in the top of a vertical plate or plank, through which water flows, -- used in measuring the quantity of flowing water.