a horizontal ring or segment of a ring, consisting of two bands that slide on each other, placed above the front axle of a carriage and designed to support the forepart of the body while allowing it to turn freely in a horizontal plane.
2.
a similar device used as a coupling to connect a semitrailer to a tractor.
3.
a similar coupling between a heavy-duty pickup truck and a camping trailer (fifth-wheel trailer) that extends over the bed of the truck.
4.
an extra wheel for a four-wheeled vehicle.
5.
a superfluous, unneeded, or unwanted person or thing: They enjoy making any outsider feel like a fifth wheel.
n. an extra and unneeded person. : I feel like such a fifth wheel around here.
Dictionary of American Slang and Colloquial Expressions by Richard A. Spears.Fourth Edition. Copyright 2007. Published by McGraw Hill.
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