What is 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 called?

lagoon — 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. (Webster's 1913.)