lagoon

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A shallow body of water, especially one separated from a sea by sandbars or coral reefs.
2. n. A shallow body of liquid waste material, as one in a dump.

Century Dictionary and Cyclopedia

1. n. An area of shallow water, or even of marshy land, bordering on the sea, and usually separated from the region of deeper water outside by a belt of sand or of sand-dunes, more or less changeable in position. Such areas are chiefly formed at the mouths of rivers which bring down considerable detrital material from adjacent elevated land—this detritus in course of time forming a complicated network of ridges separating tracts covered by shallow water, which, as the process of filling goes on tend to become converted first into marshy and finally into dry land. The best-known lagoons are those near the head nf the Adriatic, on its western side, on the outer edge of which is situated Venice, often called the “City of the Lagoons” (la citta delle lagune). The tendency of the Brenta and other small streams coming from the Alps to fill up the Venetian lagoons is so powerful that it is only by persistent and costly works of hydraulic engineering that the city has to a certain extent retained its position unchanged. A somewhat similar condition prevails at the mouth of the Rhone, where, however, the lagoons are called étangs. On the southern coast of the Baltic considerable areas of the shallow sea (called Haffe) are closed in by long crescentiform sand-banks (Nehrungen); but the conditions here are quite different from those at the head of the Adriatic, since the streams flowing over the plains of North Germany are not torrential in character. Lagoons are found in great numbers along the coast of Brazil, formed there as elsewhere by the conflict of large detritus-bearing rivers with the ocean waves and tides. In regions where Spanish is or formerly was the current language, the word lagoon is likely to be used with more latitude of meaning, since in the Spanish language laguna is applied to ordinary lakes, to the bottoms of deep bays, especially when these are more or less closed in by a narrowing of the coast-linos, so as to give rise to lake-like areas, and also to shallow, swampy, or almost dried-up lakes inland as well as near the coast.
2. n. With reference to Tuscany and some other parts of Italy, the basin of a hot spring, especially one from which borax is obtained: from the Italian use of lagone in this sense.
3. n. In occasional use, the area of still water inclosed within an atoll, which is often called a lagoon island. See atoll.

Wiktionary

1. n. A shallow body of water separated from deeper sea by a bar.

GNU Webster's 1913

1. n. A shallow sound, channel, pond, or lake, especially one into which the sea flows.
2. n. A lake in a coral island, often occupying a large portion of its area, and usually communicating with the sea. See Atoll.

WordNet 3.0

1. n. a body of water cut off from a larger body by a reef of sand or coral