Are you talking about an understudy? Understudies are people who come to rehearsals and then if the actor that was formerly hired cannot perform (due to sickness, quitting, ect.) then the understudy takes their part. I think that they are called understudies because they study the actor's lines (hence study) and are underneath the position of the actor. I hope I helped.
extra
power
Audition
Steve McQueen
Jake Gyllenhaal
Substitute for an actor.
Yes. The substitute runner is called the "pinch runner".
An official who takes the position of another official is usually called a substitute, reserve, or replacement official.
The substitute teacher is horrible.I need to substitute something with the nuts in this recipe.The manager called the substitute onto the pitch.
you can not substitute me. The director Substituted lead actor.
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Good that can be used in place of another good.
Thespian is another word for an actor or actress.
substitute
replacement
what word can I substitute for constitutes
A close substitute is a product or service you can purchase in place of another and still get the same satisfaction. There are many substitute goods available on the market.