E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
A pirate. So called from the vik or creek in which he lurked. The word is wholly unconnected with the word king. There were sea-kings, sometimes, but erroneously, called vikings, connected with royal blood, and having small dominions on the coast. These sea-kings were often vikingr or vikings, but the reverse is not true that every viking or pirate was a sea-king. (Icelandic vikingr, a pirate.)