Lagoon

lagoon
    n 1: a body of water cut off from a larger body by a reef of
         sand or coral [syn: {lagoon}, {laguna}, {lagune}]
    

lagoon \la*goon"\ (l[.a]*g[=oo]n"), n. [It. or Sp. laguna, L.
   lacuna ditch, pool, pond, lacus lake. See {Lake}, and cf.
   {Lacuna}.] [Written also {lagune}.]
   1. A shallow sound, channel, pond, or lake, especially one
      into which the sea flows; as, the lagoons of Venice.
      [1913 Webster]

   2. A lake in a coral island, often occupying a large portion
      of its area, and usually communicating with the sea. See
      {Atoll}.
      [1913 Webster]

   {Lagoon island}, a coral island consisting of a narrow reef
      encircling a lagoon.
      [1913 Webster] Lagophthalmia
    

43 Moby Thesaurus words for "lagoon":
      artificial lake, bayou lake, cistern, dam, dead water, dike, etang,
      farm pond, fishpond, freshwater lake, glacial lake, inland sea,
      laguna, lake, lakelet, landlocked water, linn, loch, lough, mere,
      millpond, millpool, nyanza, oxbow lake, plash, pond, pondlet, pool,
      puddle, reservoir, salina, salt pond, stagnant water,
      standing water, still water, sump, tank, tarn, tidal pond,
      volcanic lake, water hole, water pocket, well