- a vertical blade at the stern of a vessel that can be turned horizontally to change the vessel's direction when in motion.
- a movable control surface attached to a vertical stabilizer, located at the rear of an airplane and used, along with the ailerons, to turn the airplane.
- any means of or device for governing, directing, or guiding a course, as a leader or principle: His ideas provided a rudder for the new company.
- a pivoted vertical vane that projects into the water at the stern of a vessel and can be controlled by a tiller, wheel, or other apparatus to steer the vessel
- a vertical control surface attached to the rear of the fin used to steer an aircraft, in conjunction with the ailerons
- anything that guides or directs
