- a horizontal wheel-like structure placed over the front axle of a carriage or wagon to support it on turns
- a similar structure on the rear of the cab of a tractor-trailer, serving as a coupling for attaching the trailer
- an unnecessary or superfluous person or thing
- a. A wheel or portion of a wheel placed horizontally over the forward axle of a carriage to provide support and stability during turns.b. A similar device over the rear axle or axles of a tractor or pickup truck, serving as a coupling for a semitrailer.
- An additional wheel carried on a four-wheeled vehicle as a spare.
- An extra and unnecessary person or thing.
(plural fifth wheels)
- A type of trailer hitch, which consists of a horseshoe-shaped plate on a multi-directional pivot, with a locking pin to couple with the kingpin of a truck trailer.
- A very large truck trailer; an 18-wheeler.
- A very large trailer that is towed with a pickup truck.
- (idiomatic) Anything superfluous or unnecessary.
- As the third person along on their date, I felt like a fifth wheel.
- I felt like a fifth wheel when they started giggling and making out during dinner.