a hinged vertical airfoil mounted at the tail of an aircraft and used to make horizontal course changes
"The pilot adjusted the rudder to help the plane bank smoothly during the sharp turn."
(nautical) steering mechanism consisting of a hinged vertical plate mounted at the stern of a vessel
"The captain pulled the wheel hard to starboard, forcing the rudder against the current until the ship finally turned into the harbor."
An underwater vane used to steer a vessel. The rudder is controlled by means of a wheel, tiller or other apparatus (modern vessels can be controlled even with a joystick or an autopilot).
"The captain turned the wheel sharply to correct the ship's course after it began drifting off its intended path in the strong current."