D defs.my
Entry 2 senses Webster, 1913

lagoon

/(lȧ*go͞on")/ · la·goon · IPA /ləˈɡuːn/
01 n. A shallow sound, channel, pond, or lake, especially one into which the sea flows; as, the lagoons of Venice.
  1. 1.
    A shallow sound, channel, pond, or lake, especially one into which the sea flows; as, the lagoons of Venice.
  2. 2.
    A lake in a coral island, often occupying a large portion of its area, and usually communicating with the sea. See Atoll. See: Atoll
Phrases & compounds
Lagoon island — a coral island consisting of a narrow reef encircling a lagoon.