- a superfluous person or thing；a trailer with accommodation for camping out
noun: fifth-wheel trailer, plural noun: fifth-wheel trailers
- 1. informal a superfluous person or thing I was the fifth wheel to two sets of coupled-up friends Kayla is a fifth wheel in a group of four high-schoolers meeting at the mall food court
- 2. a trailer with accommodation for camping out they sold their house, bought a fifth wheel, and started travelling all over the US the truck was towing a thirty-foot fifth wheel trailer
- 3. a coupling between a vehicle used for towing and a trailer.
- ▪ historical a horizontal turntable over the front axle of a carriage as an extra support to prevent it tipping.