fifth wheel

[ fifth weel, hweel; often, fith ]

noun

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 carriage 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 trail·er that extends over the bed of the truck.
4. an extra wheel for a four-wheeled vehicle.
5. third wheel ( def ):

   I decided not to go along on the canoe trip with him and his friends—I’d just be a fifth wheel.

fifth wheel

noun

1. a spare wheel for a four-wheeled vehicle
2. 1. the coupling table of an articulated vehicle
   2. a steering bearing that enables the front axle of a horse-drawn vehicle to rotate relative to the body
3. a superfluous or unnecessary person or thing

fifth wheel

1. A hanger-on; a person who serves no function: “The vice president felt like a fifth wheel after his exclusion from the committee.”

Word History and Origins

Origin of fifth wheel¹

First recorded in 1870–75

Idioms and Phrases

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.”