1) An artificial water-course designed to carry water to a dam or drain marshy land of excess surface water, taking it off into a river or the sea.
1352 Cum wallić, fossata, gutterć, sewerć, pontes, calceta et gurgites aquarum de Trent et Done, Selby Abbey
1527 als well the watter dame belonynge [sic] the milne as the watter sewer for the redy passaige of the watter to and frome the seid milne, Bewerley
1540 one close called the Vevers ... overflowed the moste parte all winter with water, charged with a sewer & lyenge in common pasture from Michalmas to Martynmas, Selby Abbey. As a channel for waste matter in a town it is on record from the mid-fifteenth century.