fifth wheel

fifth wheel

n.

1.

a. A wheel or portion of a wheel placed horizontally over the forward axle of a carriage to provide support and stability during turns.

b. A similar device over the rear axle or axles of a tractor or pickup truck, serving as a coupling for a semitrailer.

2. An additional wheel carried on a four-wheeled vehicle as a spare.

3. An extra and unnecessary person or thing.

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fifth wheel

n

1. (Engineering / Mechanical Engineering) a spare wheel for a four-wheeled vehicle

2. (Engineering / Mechanical Engineering)

a.  the coupling table of an articulated vehicle

b.  a steering bearing that enables the front axle of a horse-drawn vehicle to rotate relative to the body

3. a superfluous or unnecessary person or thing

Thesaurus

Noun	1.	fifth wheel - someone or something that is unwanted and unneeded deadwood redundance, redundancy - the attribute of being superfluous and unneeded; "the use of industrial robots created redundancy among workers"
	2.	fifth wheel - an extra car wheel and tire for a four-wheel vehicle spare car wheel - a wheel that has a tire and rim and hubcap; used to propel the car
	3.	fifth wheel - a steering bearing that enables the front axle of a horse-drawn wagon to rotate bearing - a rotating support placed between moving parts to allow them to move easily