Rudder

Noun

 * 1)  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).
 * 2)  A control surface on the vertical stabilizer of a fixed-wing aircraft or an autogyro.  On some craft, the entire vertical stabilizer comprises the rudder.  The rudder is controlled by foot-operated control pedals.