a lake in Africa at the junction of four countries: Cameroon, Chad, Niger, and Nigeria. 5000 to 10,000 sq. mi. (13,000 to 26,000 sq. km) (seasonal variation).
Official name,a republic in N central Africa, E of Lake Chad: a member of the French Community; formerly part of French Equatorial Africa. 4,100,000; 501,000 sq. mi. (1,297,590 sq. km). Cap.: N'Djamena.