Kiritimati (kərĭsˈməs) [key], largest atoll in the Pacific (1990 pop. 2,537), 222 sq mi (575 sq km), in the Line Islands, one of the island groups that compose the Republic of Kiribati. It was previously called Christmas Island when it made up part of the former British colony of the Gilbert and Ellice Islands. The island's chief agricultural product is copra. The airstrip there is used an emergency runway for trans-Pacific commercial flights. The atoll was explored by Capt. James Cook in 1777, annexed by Great Britain in 1888, and included in the Gilbert and Ellice Islands colony in 1919. British nuclear tests were conducted on the atoll in 1957 and 1958 and U.S. tests in 1962.