From WordNet (r) 2.0 (August 2003) [wn]:
lagoon
n : a body of water cut off from a larger body by a reef of sand
or coral [syn: laguna, lagune]
From The Collaborative International Dictionary of English v.0.48 [gcide]:
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