costar[kō′stär′; for v., usually kō′stär′]
costar definition by Webster's New World
Webster's New World College Dictionary Copyright © 2010 by Wiley Publishing, Inc., Cleveland, Ohio. Used by arrangement with John Wiley & Sons, Inc.
any featured actor or actress given equal prominence with another or others in a film, play, etc.
Origin: co- plush star
costar definition by American Heritage Dictionary
A starring actor or actress given equal status with another or others in a play or film.tr. & intr.v. co·starred also co-starred, co·star·ring also co-star·ring, co·stars also co-stars
To act or present as a costar.