- 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
See fifth wheel in American Heritage Dictionary 4
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.
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