(noun, verb)


1. (acting) A person who shares star billing.

- The once famous actor objected to his costar having a bigger dressing room.

2. (acting) A person who slightly lacks the status to be considered a star.

- Alas, always a costar but never a star.


1. to perform with the billing of a costar.

- People thought his career was over but now he will get to costar on Broadway next month.