antechamber

ante- +‎ chamber

• (UK) IPA^(key): /ˈæntiˌt͡ʃeɪmbə/
• (US) IPA^(key): /ˈæntiˌt͡ʃeɪmbɚ/

antechamber (plural antechambers)

1. A small room used as an entryway or reception area to a larger room.
   • 2005, J. K. Rowling, Harry Potter and the Half-Blood Prince, Arthur A. Levine Books (2005), 558,

     "This is merely the antechamber, the entrance hall," said Dumbledore after a moment or two.

• anteroom