costar

noun

1. A person who shares star billing with another.

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

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

   “Alas, always a costar but never a star.”

verb

1. (intransitive)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.”

2. (transitive)To feature (a number of star performers) jointly.

   “Purchasing a snowplow transforms Homer into a new man. Mr. Burns' laziest employee suddenly becomes an ambitious self-starter who buys ad time on local television at 3:17 A.M^([sic]) (prime viewing hours, Homer gingerly volunteers, for everyone from alcoholics to the unemployable to garden-variety angry loners) and makes a homemade commercial costarring his family.”