wer

Old English wer meant a dam or an enclosure in a river, designed to trap fish or raise the water level. The word appears in the earliest English legal documents—the laws of King Ine of Wessex, written around 694 CE, mention weirs as taxable property. Owning a weir meant owning a food source, and Anglo-Saxon charters treated weirs as valuable assets.

The Domesday Book of 1086 records hundreds of weirs across England. They were essential infrastructure: low barriers of stone or woven branches that channeled fish into traps as the current pushed them downstream. Salmon weirs on the Severn, eel weirs on the Thames, herring weirs along the coast. Medieval England fed itself, in part, through weirs.

The word survived the Norman Conquest largely unchanged—one of the few Old English infrastructure terms that French did not replace. Dam came from Middle Dutch, levee from French, but weir stayed English. Perhaps because the technology was so deeply embedded in English rural life that no foreign word could displace it.

Modern civil engineering still uses weirs as flow-measurement devices. A weir of known dimensions, placed across a channel, allows engineers to calculate water flow by measuring the depth of water passing over it. The Anglo-Saxon fish trap became a precision instrument, but the word and the basic principle remain identical.