fifth wheel Hear it!

fifth wheel definition

fifth wheel

    1. a horizontal wheel-like structure placed over the front axle of a carriage or wagon to support it on turns
    2. ☆ a similar structure on the rear of the cab of a tractor-trailer, serving as a coupling for attaching the trailer
  2. an unnecessary or superfluous person or thing

Webster's New World College Dictionary Copyright © 2005 by Wiley Publishing, Inc., Cleveland, Ohio.
Used by arrangement with John Wiley & Sons, Inc.

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