Longman Dictionary of Contemporary English
The Collaborative International Dictionary
co-star \co-star\ v. t. to feature as the co-star in a performance; as, the film co-starred Robin Williams as the psychiatrist.
co-star \co-star\ v. i. to be the co-star in a performance; as, Robin Williams co-starred in the film.
Douglas Harper's Etymology Dictionary
Wiktionary
n. (alternative spelling of costar English) vb. (alternative spelling of costar English)
WordNet
n. one of two actors who are given equal status as stars in a play or film
v. feature as the co-star in a performance
be the co-star in a performance
[also: co-starring, co-starred]
Usage examples of "co-star".
Hitchcock intended to end the film with Grant about to murder his co-star, Joan Fontainea daring, and audience-upsetting climax.
Like her three co-stars Mags is something of a television name by now.
Fingerhood, Jimmy, her co-star, her husband, the movie composer she screwed in desperation the night she lost the Oscar, the cameraman whose only interest was her labia minora which he said resembled a pink tea rose, the construction worker she picked up on a dare and was let down by with a bang, even the midgetthey all agreed she was a washout in bed.
In the fight scene proper, an anoraked Lorne Guyland is given the hiding of his life, despite the fact that he surprises his sleeping co-star with a car-tool.
Soon I sink into a dream with a familiar theme, co-starring Janet Thrush.
She said she had a co-starring role, and she showed around a viewfinder.
On the far side of Jay's table I saw the handsome face of Housemartin, his co-star in the Charlotte street film library.
And so were the animators and voice actors who created his co-stars.