The Collaborative International Dictionary of English v.0.48:

Atoll \A*toll"\, n. [The native name in the Indian Ocean.]
   A coral island or islands, consisting of a belt of coral
   reef, partly submerged, surrounding a central lagoon or
   depression; a lagoon island.
   [1913 Webster]

WordNet (r) 3.0 (2006):

atoll
    n 1: an island consisting of a circular coral reef surrounding a
         lagoon

Moby Thesaurus II by Grady Ward, 1.0:

20 Moby Thesaurus words for "atoll":
   ait, archipelago, bar, cay, continental island, coral head,
   coral island, coral reef, holm, insularity, island, island group,
   islandology, isle, islet, key, oceanic island, reef, sandbank,
   sandbar



The Free On-line Dictionary of Computing (30 December 2018):

Acceptance, Test Or Launch Language
ATOLL

    (ATOLL) The language used for automating the
   checking and launch of Saturn rockets.

   ["SLCC ATOLL User's Manual", IBM 70-F11-0001, Huntsville AL
   Dec 1970].

   (2000-04-03)