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fifth wheel

(road transport) A type of trailer hitch, which consists of a horseshoe-shaped plate on a multidirectional pivot, with a locking pin to couple with the kingpin of a truck trailer.

ˌfɪfθ ˈʍiːlCurrent162 viewsLast reviewed Jun 29, 2026+ Add a definition
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#1·Apr 27, 2026

(road transport) A type of trailer hitch, which consists of a horseshoe-shaped plate on a multidirectional pivot, with a locking pin to couple with the kingpin of a truck trailer.

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  • “I’ve driven end to end pulling a fifth wheel several times. It takes 3 days going 65 mph.”

In most forms of semi-trailers a great deal of time is wasted in connecting the trailer to the tractor or pulling vehicle. Most of the connecting gears are some form of fifth wheel, consisting of two horizontal circular bands of iron, on…
Origin: From the fact that since many vehicles such as carriages, coaches, wagons, prime movers, and trucks generally have four wheels on which they move, this component which resembles a wheel is the fifth. * (anything superfluous or unnecessary): Sense 3 refers to the fact that a fifth wheel is not needed for a four-wheeled vehicle to operate. Origin information sourced from Wiktionary contributors (CC BY-SA 4.0).
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  • “Lippert Venture Fifth Wheel Landing Gear Motor, Standard Replacement Motor, No Assembly Required, Motor Only - 142178 #RVRepair #FifthWheel #LandingGear #ReplacementMotor #RVAccessories #RVParts”

    — Bluesky· May 2026
  • “I’ve driven end to end pulling a fifth wheel several times. It takes 3 days going 65 mph.”

    — Bluesky· May 2026
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#2·Apr 27, 2026

(idiomatic, informal) Anything superfluous or unnecessary.

From the blow-back tank, the fluid is piped into a larger tank commonly known as a fracturing (frac) tank or wheely tank. This is a large, 21,000-gallon tank mounted on wheels and provided with a fifth wheel for towing from jobsite to jo…
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#3·Apr 27, 2026

(road transport, historical) A horizontal wheel or segment of a wheel above the front axle and beneath the body of a carriage, forming an extended support to prevent it from overturning.

The semi-trailers are equipped with hydraulic brakes which operate through the king pin of the fifth wheel. The booster-controlled fifth wheel gives full and complete cab control of all braking and coupling operations.
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