| 1. | 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 body while allowing it to turn freely in a horizontal plane. |
| 2. | a similar device used as a coupling to connect a semitrailer to a tractor. |
| 3. | a similar coupling between a heavy-duty pickup truck and a camping trailer (fifth-wheel trailer) that extends over the bed of the truck. |
| 4. | an extra wheel for a four-wheeled vehicle. |
| 5. | a superfluous, unneeded, or unwanted person or thing: They enjoy making any outsider feel like a fifth wheel. |
| fifth wheel n.
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A hanger-on; a person who serves no function: “The vice president felt like a fifth wheel after his exclusion from the committee.”
fifth wheel
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fifth wheel
An extra and unnecessary person or thing, as in He was the only one without a date, so he felt like a fifth wheel. This expression, which alludes to an unneeded wheel on a four-wheel vehicle, may have originated as long ago as 1631, when Thomas Dekker wrote Match Me in London: "Thou tiest but wings to a swift gray Hounds heel, And addest to a running Chariot a fifth wheel."
