Someone with whom one performs together, as a member of a cast
2007 June 14, Melena Ryzik, “Unwelcome at Home, Student Play Is a Hit in New York”, in The New York Times:
A few feet away, her friend and castmate Tara Ross, also 18, was applying makeup; outside their door, a couple of boys were sacked out on a couch, studying notes in binders.