Skagerrak

Of Dutch origin from the 17th century. From the 18th century and on, Skagerrak was the official name on maps, whereas Kattegatt was the vulgar name between sailors. In time, Kattegatt came to be the more common name and Skagerrak only meant the outer part of the area, between Skagen and Norway. In the 19th century the names were still used synonymously. Skagerrak comes from the name Skagen and a word meaning “straight stretch” (rak, from Dutch or Low German; in modern Dutch rak is a straight stretch in an otherwise sinuous waterway; in modern sailing the distance to be sailed between two points), so the word means “the straight passage at Skagen”.

来源：wiktionary