from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. Nickname for a sailor in the Royal Navy.
From Jack, a common name for a sailor plus tar, used to waterproof sails as well as the seams between planks on wooden ships (1781). Sailors also used tar for clothing, grooming: their coats and hats, were made of the waterproof fabric called tarpaulin; seamen commonly pleated their long hair into a pigtail and smeared it with high grade tar to prevent it getting caught in the ship's equipment, a practice that continued until the early 20th century. Often a sailor's hands would be stained with tar. (Wiktionary)