A cast member who learns another actor's role and steps in when that actor is out.
An understudy usually plays a smaller part or sings in the ensemble every night while also knowing one or more leading roles. When a principal actor is sick, injured or on vacation, the understudy goes on. Theaters post a slip in the program or a sign in the lobby when this happens. Seeing an understudy is not a lesser night; many careers began with a surprise performance in a lead.
Also seen as: understudies, understudying