Focus on the pronunciation of costar
English definition of “costar”
/ˈkoʊˌstɑr/ n [C]
› a famous actor appearing with one or more other famous actors in a film or a play costar
/ˈkoʊˌstɑr/, /ˈkoʊˈstɑr/ v [I/T] (-rr-) › [I] Bergman and Bogart costarred in "Casablanca."