an island of France, off the coast of the department of Vendée, separated from the mainland by a channel about one mile in breadth, which is nearly dry at low-water. Its length is about ten miles, greatest breadth three; area about seventy square miles, of which only about one-fifth is cultivated. This part is very fertile; and the rest of the surface is occupied chiefly by pasture ground and salt marshes. The island lies generally somewhat below the level of the sea, and is protected from inundation by embankments. The principal productions are salt, corn, beans, and some wine. On the east coast stands a town of the same name, which is well built, and has an old castle and a harbour. Pop. 7011.