antechamber
/ˌæntɪˈtʃæm.bər/Definitions
1. noun
A room or space that leads to a larger room, often used for waiting or receiving guests.
“The guests had to wait in the antechamber before being introduced to the host.”
2. noun
A preliminary or introductory section or part of something.
“The antechamber to the main plot of the novel was full of suspense and intrigue.”