What is the synonym of a rudder?

There isn't a single perfect synonym for "rudder", as it's a very specific nautical term. However, depending on the context, you could use:

* Steering mechanism: This is a more general term that encompasses the rudder and other steering devices.

* Helm: This refers to the entire steering system, including the rudder, wheel, and other components.

* Direction control: This is a broader term that applies to any mechanism used to change direction.

* Tailfin (on an airplane): This is analogous to a rudder on a plane, but not the same.

The best synonym will depend on the specific context in which you are using the word "rudder."