A frame of timber, stone, or other matter, serving to retain and raise the water of a river, etc, and, on occasion, to let it pass. Such is the sluice of a mill, which stops and collects the water of a rivulet, etc, to let it fall, at length, in the greater plenty upon the mill wheel; such also are those used as vents, ordrains,todischarge water off land. See Tide-mill, Water-wheel, etc.