1. a ring-shaped coral reef or chain of coral islands surrounding a lagoon

Examples

• The Maldives consists of many beautiful atolls in the Indian Ocean.
• Scientists studied the coral growth on the remote atoll.
• The plane flew over a perfect circular atoll with crystal-clear water in the center.
• Many Pacific atolls are threatened by rising sea levels.
• The atoll’s lagoon provided a safe harbor for the sailing expedition.
• Bikini Atoll was used for nuclear testing in the 1940s and 1950s.