rudder

noun

1. An underwater vane used to steer a vessel. The rudder is controlled by means of a wheel, tiller or other apparatus (modern vessels can be controlled even with a joystick or an autopilot).
2. A control surface on the vertical stabilizer of a fixed-wing aircraft or an autogyro. On some craft, the entire vertical stabilizer comprises the rudder. The rudder is controlled by foot-operated control pedals.
3. A riddle or sieve.
4. (figuratively)That which resembles a rudder as a guide or governor; that which guides or governs the course.

   “For rhyme the rudder is of verses,/With which, like ships, they steer their courses.”

5. The tail of an otter.

   “He sniffed Tarka’s hair from rudder to neck, and his nose remained at the neck. It was a strange smell, and he sniffed carefully, not wanting to touch the fur with his nostrils.”