third wheeler 

When there is a couple together, and one extra person there without a date, so they are 'third-wheeling' the couple.

Mary: You and Your boyfriend (Jack) go to the movies together.
Wendy: It will be boring without you though, can't you come?
Mary: Only if we invite another person so Im not a third wheeler

third wheeler by RRRRRRAAAAACCCCCHHHHH September 30, 2013

Third Wheeler 

Someone who dedicates their lives to a couple by being single and hanging out with them.

Do you see that guy following that couple over there, yeah well he's a third wheeler.

Third Wheeler by BobbyExDeeDee September 12, 2015

third wheeler 

A third wheeler is somebody that tags along with camila cabello and shawn mendes when they're out. They're so sickening cute together, that you just look at them, feeling lonely, being a third wheeler.

shawn and camila were at the beach and connor was a third wheeler

third wheeler by memeing July 29, 2019