understudy

Universal Words noun, verb noun (plural understudies) ~ (to sb) an actor who learns the part of another actor in a play so that they can play that part if necessary: She worked as an understudy to Elaine Page. verb (understudies, understudying, understudied, understudied) [VN] to learn a part in a play as an understudy; to act as an understudy to sb: She once understudied Marilyn Monroe.