from The American Heritage® Dictionary of the English Language, 4th Edition
- n. A ringlike coral island and reef that nearly or entirely encloses a lagoon.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. A type of island consisting of a ribbon reef that nearly or entirely surrounds a lagoon and supports, in most cases, one to many islets on the reef platform. Atolls have a unique geology, so not all islands with a reef and a lagoon are atolls.
from the GNU version of the Collaborative International Dictionary of English
- n. A coral island or islands, consisting of a belt of coral reef, partly submerged, surrounding a central lagoon or depression; a lagoon island.
from The Century Dictionary and Cyclopedia
- n. A coral island, consisting of a strip or ring of coral surrounding a central lagoon.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- n. an island consisting of a circular coral reef surrounding a lagoon
Maldivean atolu; probably akin to Sinhalese ätul, interior (from the interior lagoon), probably from Sanskrit *antala-, interior, variant of antara-.(American Heritage® Dictionary of the English Language, Fourth Edition)
From Malayalam അതൊലു (atolu, "reef") and Dhivehi އބތަލ (ab-tal), from Persian آبتل (āb-tal, "water-hillock") (Wiktionary)