'co-star' definitions:

Definition of 'co-star'

(from WordNet)
noun
One of two actors who are given equal status as stars in a play or film
verb
Feature as the co-star in a performance
verb
Be the co-star in a performance

Definition of 'co-star'

From: GCIDE
  • 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. [WordNet 1.5]

Definition of 'co-star'

From: GCIDE
  • co-star \co-star\ v. i. to be the co-star in a performance; as, Robin Williams co-starred in the film. [WordNet 1.5]