The word "rudder" commonly refers to the movable part in the rear of a vessel that helps control its direction. However, there are several other words that can be used in place of "rudder" to describe this important tool. One alternative is "tiller," which is often found on smaller boats and consists of a long handle that the helmsman uses to steer the vessel. "Steering oar" is another synonym, which is a type of rudder used on ancient ships and wooden rowboats. Other options include "helm" or "steering wheel" which are devices used on larger vessels to control the rudder.