Stand in and Walk-on

Stand in verb - To serve as a replacement usually for a time only.

Walk-on and stand in are semantically related. in person who performs topic. In some cases you can use "Walk-on" instead a noun "Stand in", when it comes to topics like person who acts in performance.

Walk-on noun - Plays a small part in a dramatic production.

Stand in and walk-on are semantically related. Sometimes you can replace term "Stand in" with "Walk-on", this terms are similar.