WordNet (r) 3.0 (2006):

coral reef
    n 1: a reef consisting of coral consolidated into limestone

Moby Thesaurus II by Grady Ward, 1.0:

49 Moby Thesaurus words for "coral reef":
   ait, archipelago, atoll, bank, bar, bill, breakwater, cape, cay,
   chersonese, continental island, coral head, coral island, delta,
   flat, ford, foreland, head, headland, holm, hook, insularity,
   island, island group, islandology, isle, islet, key, mull, naze,
   ness, oceanic island, peninsula, point, promontory, reef, sandbank,
   sandbar, sandspit, shallow, shallows, shelf, shoal, shoal water,
   spit, spur, tidal flats, tongue, wetlands