fifth wheel

Definitions

Cars & Driving

  • noun an additional wheel attached to the rear of a vehicle being road-tested which drives a highly accurate speed-measuring instrument
  • noun in an articulated vehicle, the generally circular pad at the rear of the tractor unit on which the front end of the trailer is mounted and which is able to turn when a corner is being negotiated

Construction

  • The swivel connection between highway-type tractors and semi-trailers.

Slang

  • noun a superfluous or intrusive extra person, an unnecessary thing. The phrase is American in origin.
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