The word "Jack" comes from the Middle English word "jakke", which was a short, sleeveless coat or jacket often worn by sailors and peasants. Over time, the word came to be used as a generic term for a small flag, especially one flown from the bowsprit of a ship. However, there seems to be a lack of concrete information explaining the word 'Jack' when referencing union jack though Jack was commonly used for small flags at the time. So further analysis needs to be done