Sail

1. A piece of fabric attached to a vessel and arranged such that it causes the wind to drive the vessel along. Sails are typically attached to the vessel and manipulated by sailors via a combination of mast, spars, and ropes.
2. The power harnessed by a sail or sails to propel a vessel.
3. To use sail power to propel a vessel.
4. A trip in a boat or ship, especially a sailboat or sailing ship.
5. In American usage, a tower-like structure on the dorsal (topside) surface of submarines constructed since the mid-20th century—similar in appearance to a fabric sail or fin, and originally containing instruments and controls for the periscopes to direct the submarine and launch torpedo attacks. Modern sails or fins do not perform these functions.