lagoon (n.) Look up lagoon at Dictionary.com
1670s, lagune, earlier laguna (1610s), from French lagune or directly from Italian laguna "pond, lake," from Latin lacuna "pond, hole," from lacus "pond" (see lake (n.1)). Originally in reference to the region of Venice; applied 1769 (by Capt. Cook) to the lake-like stretch of water enclosed in a South Seas atoll. Also see -oon.