fifth wheel

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.
 * Sense 3 refers to the fact that a fifth wheel is not needed for a four-wheeled vehicle to operate.

Noun

 * 1)  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.
 * 2) 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.
 * 3)  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.
 * 4)  Anything superfluous or unnecessary.
 * 1) 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.
 * 2)  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.
 * 3)  Anything superfluous or unnecessary.
 * 1)  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.
 * 2)  Anything superfluous or unnecessary.
 * 1)  Anything superfluous or unnecessary.
 * 1)  Anything superfluous or unnecessary.
 * 1)  Anything superfluous or unnecessary.

Translations

 * Danish: sættevognskobling
 * French:
 * German: Sattelkupplung
 * Norwegian:
 * Bokmål: svingskive
 * Nynorsk: svingskive
 * Spanish: quinta rueda
 * Swedish:


 * Amharic:
 * Arabic: الصنيَة
 * Chinese:
 * Mandarin:, , ,
 * Czech: ,
 * Danish: femte hjul
 * Dutch: 't vijfde wiel
 * Finnish: kolmas pyörä
 * French:
 * Georgian: მეხუთე ბორბალი
 * German: fünftes Rad, fünftes Rad am Wagen
 * Hungarian:, ötödik kerék
 * Icelandic: aðskotadýr
 * Italian: ultima ruota del carro
 * Japanese: 無用の長物, 長物
 * Korean:
 * Lithuanian: penkta koja
 * Polish:
 * Portuguese: quinta roda,
 * Romanian: a cincea roată la căruță
 * Russian: (как теле́ге) пя́тое колесо́, (как соба́ке) пя́тая нога́
 * Slovak: piate koleso u voza
 * Spanish: quedarse tocando el violín
 * Swedish:
 * Vietnamese: