from The American Heritage® Dictionary of the English Language, 4th Edition
- n. A starring actor or actress given equal status with another or others in a play or film.
- transitive v. To act or present as a costar.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. A person who shares star billing.
- n. A person who slightly lacks the status to be considered a star.
- v. To perform with the billing of a costar.
co- + star (Wiktionary)