The word ‘lagoon’; highlights an interesting habit of the English language; when borrowing words from French, we loved to add emphasis and our own special touch – in this case (and many with many other words borrowed from French), it’s replacing a perfectly good word ending with ‘oon’.
The word borrowed here was ‘lagune’ which the French, in turn, had got from Italian, their word being ‘laguna’, was a term used to describe Venice. ‘Laguna’ has its origins in the Latin word ‘lacuna’, which meant ‘pond’. The Italian’s and the French were essentially describing Venice as ‘pond-like’.
Captain Cook brought the word to Britain in around 1600 when he described a body of water enclosed in a coral reef.