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3.
The meal between dinner and breakfast.

Designed for hunger at late hours of the night, most commonly used by people with the munchies, or teenagers sneaking out for midnight cravings.
"Let's head over to Taco-Waco for our Fourth Wheel, we'll get quesadillas and some queso, they don't close until 1"

"The T.H.C in my system is making my stomach feel empty, let's hit Steak-N-Bake and enjoy their 24/7 Fourth Wheel service!"
by Juicy Mane June 02, 2006
 
1.
A second third wheel, usually used to balance out a third-wheel situation; someone added to a group of three so no one is left alone.
Jimmy: "Hey Bobby, you should invite George as a fourth wheel so that Harold isn't left out."

Bobby: "Yeah, I'd hate having to leave Harold as a third wheel."

Harold: "Thanks, I think."
by catsonmeth October 16, 2012
 
2.
A third wheel third wheeling a third wheeling couple.
Basically a couple goes on a date. A second couple third wheels. A third wheeler third wheels the second couple. The Third wheeler fourth wheels the first couple
by immajewbox July 23, 2010