A ringlike coral island and reef that nearly or entirely encloses a lagoon.(noun)
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Use "atoll" in a sentence
"The atoll is on admiralty charts as Hikihoho, discovered by Bougainville [Louis Antoine de Bougainville, 1729-1811, French soldier and explorer, the first Frenchman to circumnavigate the world] but called Parlay after old Parlay, a wizard with pearls who never parts with a pearl and stores hundreds of ton of shell."
"The ring-like shape of the atoll is the result of coral reefs building up around a former volcanic island."
"The rim of the atoll is a karst structure; there is also a quantity of exposed coral rock and extensive sand dunes and rubble to the southwest."