A medieval skipper is a privateer or captain of a vessel. A privateer was the captain of a ship who hunted pirates or enemy merchant vessels during wartime while being sanctioned by the government.
A medieval skipper is the master of a vessel or ship. Often, skippers were tasked by their governments to find and destroy pirating vessels or merchant ships. The skippers then kept the cargo of the ships they plundered.
The term skipper was found as early as the 1300s in the "Canterbury Tales" by Geoffrey Chaucer. In this book, Skipper was one of the characters, and was portrayed as an immoral man who stole cargo, smuggled and had people walk the plank.
According to Reference.com, the term skipper comes from the middle English Dutch term "schip" for ship, with English speakers pronouncing it with a hard "k" sound. The term has been around for centuries and is still commonly used in reference to boats. For instance, skipper was once an actual rank in the British Royal Naval Reserve. It is still used as a slang term in the U.S. Navy and Marine Corps when talking about commanding officers. It is also used in civilian circles when it comes to recreational boats.