1. third wheel - Noun
2. third wheel - Verb
(idiomatic) A person or thing that serves no useful purpose.
(idiomatic) An unwanted third party accompanying two people on a date.
third-wheel (third-person singular simple present third-wheels, present participle third-wheeling, simple past and past participle third-wheeled)
(transitive, intransitive) To act as a third wheel; to accompany two people on a date.
third-wheel