WordNet (r) 3.0 (2006):

sandbank
    n 1: a submerged bank of sand near a shore or in a river; can be
         exposed at low tide

Moby Thesaurus II by Grady Ward, 1.0:

42 Moby Thesaurus words for "sandbank":
   ait, archipelago, atoll, bank, bar, cay, continental island,
   coral head, coral heads, coral island, coral reef, flat, ford,
   holm, insularity, ironbound coast, island, island group,
   islandology, isle, islet, key, ledges, lee shore, oceanic island,
   pitfall, quicksands, reef, rockbound coast, rocks, sandbar, sands,
   shallow, shallows, shelf, shoal, shoal water, shoals, tidal flats,
   undercurrent, undertow, wetlands