- a horizontal ring or segment of a ring, consisting of two bands that slide on each other, placed above the front axle of a carriage and designed to support the forepart of the carriage body while allowing it to turn freely in a horizontal plane.
- a similar device used as a coupling to connect a semitrailer to a tractor.
- a similar coupling between a heavy-duty pickup truck and a camping trailer (fifth-wheel trail·er ) that extends over the bed of the truck.
- an extra wheel for a four-wheeled vehicle.
- third wheel: I decided not to go along on the canoe trip with him and his friends—I’d just be a fifth wheel.
- a spare wheel for a four-wheeled vehicle
- the coupling table of an articulated vehicle
- a steering bearing that enables the front axle of a horse-drawn vehicle to rotate relative to the body
- a superfluous or unnecessary person or thing
