atoll
US /ˈæt.ɑːl/
UK /ˈæt.ɑːl/

1.
環礁
a ring-shaped coral reef or island or a string of coral islands enclosing a shallow lagoon
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The divers explored the vibrant marine life around the atoll.
潛水員們探索了環礁周圍充滿活力的海洋生物。
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Many Pacific islands are formed by atolls.
許多太平洋島嶼是由環礁形成的。