atoll (n.) Look up atoll at Dictionary.com
"island consisting of a strip or ring of coral around a central lagoon," 1620s, atollon, from Malayalam (Dravidian) atolu "reef," which is said to be from adal "closing, uniting." Watkins writes, "Perhaps ultimately from Sanskrit antara-, interior," and thus related to English in, Latin intra, Greek entos. The original use was in reference to the Maldives. Popularized in present form by Darwin's writings.