atoll
n.n. a ring-shaped island made of coral that forms around a lagoon. It is usually found in the ocean and is surrounded by water.
n. a ring-shaped coral island or reef, typically surrounding a lagoon. Formed by the growth of coral on the rim of a volcanic crater or on the edge of a submerged island.
The island is a small atoll in the middle of the ocean.
Many of the islands in the Pacific are actually atolls formed by coral reefs over thousands of years.
The unique ecosystem of the atoll is maintained by the delicate balance between the coral reef and the surrounding lagoon, which provides a protected habitat for various marine species.
Borrowed from Portuguese atol, from Dhivehi އަތޮޅު (atoḷu), possibly from Prakrit 𑀲𑀁𑀢𑀻𑀞 (saṃtīṭha), from Sanskrit संतीर्थ (saṃtīrtha, “level ford”). The traditional etymology from Persian آبتل (âb-tal, “water-hillock”) is unlikely.