rud·der / ˈrədər/ • n. a flat piece, usu. of wood, metal, or plastic, hinged vertically near the stern of a boat or ship for steering. ∎  a vertical airfoil pivoted from the horizontal stabilizer of an aircraft, for controlling movement around the vertical axis. ∎  application of a rudder in steering a boat, ship, or aircraft: bring the aircraft to a stall and apply full rudder a small amount of extra rudder.

aircraft rudder

rudder †steering oar OE.; steering-gear mounted in a boat or ship XIV. OE. roðer = MLG., MDu. rōder (Du. roer), OHG. ruodar, (G. ruder):- WGmc. *rōþra-, rel. to ROW2.