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.
a similar device used as a coupling to connect a semitrailer to a tractor.
a similar coupling between a heavy-duty pickup truck and a camping trailer (fifth-wheel trailer) that extends over the bed of the truck.
an extra wheel for a four-wheeled vehicle.
a superfluous, unneeded, or unwanted person or thing: They enjoy making any outsider feel like a fifth wheel.
An extra and unnecessary person or thing, as in He was the only one without a date, so he felt like a fifth wheel. This expression, which alludes to an unneeded wheel on a four-wheel vehicle, may have originated as long ago as 1631, when Thomas Dekker wrote Match Me in London: “Thou tiest but wings to a swift gray Hounds heel, And addest to a running Chariot a fifth wheel.”
