An atoll is an island formed by a ring-shaped coral reef encircling a lagoon. The word comes from the language of the Maldives, an island chain in the Indian Ocean famous for gorgeous beaches and coral reefs.

The word atoll appeared in English in the early 17th century, when the British and the Dutch were vying for control of Indian Ocean trade. You may have heard of Bikini Atoll, in the South Pacific — where the U.S. did extensive nuclear testing in the 1940s and 1950s. Its people were moved to neighboring atolls but haven’t been able to return because of lingering radiation. Even so, Bikini Atoll has become a destination for divers interested in WWII shipwrecks.

Definitions of atoll
  1. noun
    an island consisting of a circular coral reef surrounding a lagoon
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    an atoll in the Marshall Islands; formerly used by the United States as a site for testing nuclear weapons
    an atoll in the Marshall Islands; site of an amphibious assault in World War II; later used temporarily by the United States to test atomic bombs
    an atoll in the western Marshall Islands that was used as a Japanese air and naval base during World War II
    Midway Islands
    an atoll in the Hawaiian Islands some 1300 miles to the northwest of Honolulu; site of an important United States naval base
    type of:
    coral reef
    a reef consisting of coral consolidated into limestone
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