fifth wheel

== English == === 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. === Alternative forms === 5th wheel === Pronunciation === (Received Pronunciation) IPA(key): /ˌfɪfθ ˈʍiːl/, /-ˈwiːl/ (General American) IPA(key): /ˌfɪfθ ˈʍil/, /-ˈwil/ === Noun === fifth wheel (plural fifth wheels) (chiefly US) (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. In full, fifth-wheel trailer: a large caravan or travel trailer that is connected to a pickup truck for towing by a hitch similar to the one described in sense 1 located in the center of the truck's bed. (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. (idiomatic, informal) Anything superfluous or unnecessary. Synonyms: spare tool, third wheel (idiomatic) An unwanted person accompanying two couples on a double date. Coordinate term: third wheel ==== Translations ==== === Notes === === Further reading === caravan (towed trailer) on Wikipedia.Wikipedia fifth-wheel coupling on Wikipedia.Wikipedia fifth wheel (disambiguation) on Wikipedia.Wikipedia “fifth-wheel, n.” under “fifth, adj. and n.”, in OED Online ⁠, Oxford: Oxford University Press, 1896. “fifth wheel, n.”, in Lexico, Dictionary.com; Oxford University Press, 2019–2022.