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: Webster's Revised Unabridged Dictionary (1913)