fifth wheel

noun
/ˌfɪfθ ˈʍiːl/UK/ˌfɪfθ ˈʍil/US

Etymology

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.

Definitions

  1. A type of trailer hitch, which consists of a horseshoe-shaped plate on a multidirectional…

    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.

    • 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.
  2. A horizontal wheel or segment of a wheel above the front axle and beneath the body of a…

    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.

    • For greasing the axles and fifth wheel, use castor-oil. It is not necessary to put on a great deal. [...] The fifth wheel should be looked after, and not be allowed to become entirely dry.
  3. Anything superfluous or unnecessary.

    • I felt like a fifth wheel when both of them started giggling and making out during dinner.
    • A subjunctive mode should no more exist in the English grammar, than a fifth wheel be given to a wagon.
    • Why I'm of no more use in my own house, than a fifth wheel would be to a wagon.

The neighborhood

Vish — recursive loop

No curated loop yet for fifth wheel. Loops are being traced one word at a time while the ingestion pipeline matures.

sense glosses and etymology drawn from English Wiktionary · source · CC-BY-SA