NEATH, a parliamentary and municipal borough and river-port of Glamorgan, south Wales, on a navigable river of the same name, 8 miles E. N. E. of Swansea. It is believed to stand on the site of the Roman station Nidum; and near it are the remains of an ancient castle, burned in 1231, and ruins of Neath Abbey. There are at Neath, which is one of the Swansea boroughs, extensive copper and tin-plate works and iron foundries, and chemicals are manufactured. Pop. about 18,000.