costar

/K OW1 S T AA0 R/
noun
  1. 1

    A person who shares star billing

    โ€œThe once famous actor objected to his costar having a bigger dressing room.โ€

  2. 2

    A person who slightly lacks the status to be considered a star

    โ€œAlas, always a costar but never a star.โ€

verb
  1. 1

    To perform with the billing of a costar.

    โ€œPeople thought his career was over but now he will get to costar on Broadway next month.โ€

Source: https://en.wiktionary.org/wiki/costar