an island in the Indian Ocean, off the E coast of Africa: settled by Persians and Arabs from the 7th century onwards; became a flourishing trading centre for slaves, ivory, and cloves; made a British protectorate in 1890, becoming independent within the Commonwealth in 1963 and a republic in 1964; joined with Tanganyika in 1964 to form the United Republic of Tanzania. Pop: 622 459 (2002)