understudy
under|study /'ʌndərstʌdi/ (understudies)
[N-COUNT]
An actor's or actress's understudy is the person who has learned their part in a play and can act the part if the actor or actress is ill.
He was an understudy to Charlie Chaplin on a tour of the USA.
[N-COUNT]
An actor's or actress's understudy is the person who has learned their part in a play and can act the part if the actor or actress is ill.
He was an understudy to Charlie Chaplin on a tour of the USA.