Amateur and Walk-on

Amateur noun - A person who regularly or occasionally engages in an activity as a pastime rather than as a profession.

Walk-on and amateur are semantically related In some cases you can use "Walk-on" instead a noun "Amateur".

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

Amateur and walk-on are semantically related in person who performs topic. Sometimes you can use "Amateur" instead a noun phrase "Walk-on".