Preliminary and Walk-up

Preliminary noun - A performance, activity, or event that precedes and sets the stage for the main event.

Walk-up and preliminary are semantically related In some cases you can use "Walk-up" instead a noun "Preliminary".

Walk-up noun - An apartment building without an elevator.

Preliminary and walk-up are semantically related in short preliminary event topic. Sometimes you can use "Preliminary" instead a noun phrase "Walk-up".