third wheel

/TH ER1 D W IY0 L/
noun
  1. 1

    (idiomatic) A third party, usually unwanted, accompanying two people on a date.

  2. 2

    (idiomatic) An individual or object that serves no useful purpose.

  3. 3

    Used other than figuratively or idiomatically: see third, wheel.

verb
  1. 1

    Alternative form of third-wheel. [(ambitransitive) To act as a third wheel; to accompany two people, unwanted, on a date.]