Source : Webster's Revised Unabridged Dictionary (1913)

Lagoon \La*goon"\, 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.

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

   {Lagoon island}, a coral island consisting of a narrow reef
      encircling a lagoon.

Source : WordNet®

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