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fifth wheel

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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 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.
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Origin of fifth wheel

First recorded in 1870–75
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018
British Dictionary definitions for fifth wheel

fifth wheel

noun
  1. a spare wheel for a four-wheeled vehicle
    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
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Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
fifth wheel in Culture

fifth wheel

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

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The New Dictionary of Cultural Literacy, Third Edition Copyright © 2005 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

Idioms and Phrases with fifth wheel

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.”

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The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.