a mountainous island in W Indonesia, in the Greater Sunda Islands, separated from the Malay Peninsula by the Strait of Malacca: Dutch control began in the 16th century; joined Indonesia in 1945. Northern coastal areas, esp Aceh province, suffered devastation as a result of the Indian Ocean tsunami of December 2004. Pop: 42 409 510 (2000). Area: 473 606 sq km (182 821 sq miles)