Definition

Noun: 1. A steering bearing that enables the front axle of a horse-drawn wagon to rotate: A mechanical device, typically a horizontal circular plate, that allows the front axle and wheels of a wagon or carriage to turn independently of the wagon's body. 2. An extra car wheel and tire for a four-wheel vehicle: A spare tire, carried for use in case one of the four main tires becomes flat or damaged. 3. Someone or something that is unwanted and unneeded: A person or thing that is superfluous, unnecessary, or feels out of place in a particular situation, especially when the social or functional group is already complete without them.

Usage Examples

• Noun (Mechanical Device):
  • The old carriage was restored, including its original fifth wheel.
  • The fifth wheel allows the front wheels to pivot smoothly.
• Noun (Spare Tire):
  • Make sure the fifth wheel in the trunk is properly inflated.
  • After the puncture, we had to stop and put on the fifth wheel.
• Noun (Superfluous Person/Thing):
  • At the dinner party with two couples, I felt like a fifth wheel.
  • The new committee member was treated as a fifth wheel, as the core group had already made all the decisions.

Advanced Usage

• The metaphorical sense (an unwanted person) is the most common contemporary usage. It often describes a person who joins a group of couples or an even-numbered, established pair, making the group's dynamic awkward.
• The term can also apply to objects or ideas that are redundant. For example:

Variants and Related Words

• Fifth-wheel coupling (noun): A type of hitch for connecting a semi-trailer to a tractor truck, which functions on a similar pivoting principle as the original horse-drawn device. This is a specific technical compound term.
• Spare tire (noun): The more common modern term for the extra wheel carried in a vehicle.
• Tagalong (noun): A person who follows others, especially when not invited.

Synonyms

• Superfluous: Exceeding what is sufficient or necessary.
• Redundant: No longer needed or useful; superfluous.
• Surplus: An amount of something left over when requirements have been met; an excess.
• Odd one out: A person or thing differing from the other members of a group.

Related Idioms

• A third wheel: A very similar idiom used specifically when a single person is with a couple, making them feel superfluous. ("Fifth wheel" is often used when a single person is with two couples, or any odd person in an even group).
• To be/dead wood: A person or thing that is no longer useful or productive.

Noun

1. a steering bearing that enables the front axle of a horse-drawn wagon to rotate
2. an extra car wheel and tire for a four-wheel vehicle
3. someone or something that is unwanted and unneeded