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Fifth wheel
Definitions
- 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. US
"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, one fitting on top of the other, with grease between and with a bolt or king-pin dropped through holes in the hubs or center bosses of both parts of the fifth wheel."
- 2 a steering bearing that enables the front axle of a horse-drawn wagon to rotate wordnet
- 3 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. US
"Fifth-wheel hitching is a simple affair compared to trailer coupling. Choose a quality hitch and don't overburden an inadequate pickup truck with a big fifth wheel and you're almost in business."
- 4 an extra car wheel and tire for a four-wheel vehicle wordnet
- 5 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. US, historical
"Full fifth-wheels have become quite frequent of late, and it may not be out of place to make a few remarks on their merits as compared with half fifth-wheels. With the exception of heavy coaches and rockaways, nearly all vehicles were until lately made with half fifth-wheels; but at present we find nearly all the different kinds of work, such as landaus, clarences, coaches, landaulets, T-carts, and coupés, made with full fifth-wheels."
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- 6 someone or something that is unwanted and unneeded wordnet
- 7 Anything superfluous or unnecessary. US, idiomatic, informal
"I felt like a fifth wheel when both of them started giggling and making out during dinner."
- 8 Anything superfluous or unnecessary.; An unwanted person accompanying two couples on a double date. US, idiomatic, informal
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.
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Unscramble this word: fifthwheel