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
by RRRRRRAAAAACCCCCHHHHH September 30, 2013
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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
by memeing July 30, 2019
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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.
by BobbyExDeeDee August 8, 2015
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