The definition of a rudder is a moveable flat and wide piece of wood or metal used for steering or directing.(noun)
An example of a rudder is what helps an aircraft direct its course from left to right.
See rudder in Webster's New World College Dictionary
Origin: ME rother < OE; akin to Ger ruder: see row
See rudder in American Heritage Dictionary 4
Origin: Middle English ruder
Origin: , from Old English rōther, steering oar; see erə- in Indo-European roots.
Learn more about rudder