[rud.der] n [ME rother, fr. OE rother paddle; akin to OE rowan to row] (14c) 1: a flat piece or structure of wood or metal attached upright to the stern of a boat or ship so that it can be turned causing the vessel's head to turn in the same direction
2: a movable auxiliary airfoil on an airplane usu. attached at the rear end that serves to control direction of flight in the horizontal plane--see airplane illustration
3: a guiding force or strategy -- rud.der.less adj