antechamber

noun

Etymology: From Middle French antichambre, with remodelling after ante- and chamber. By surface analysis, ante- + chamber.

1. A small room used as an entryway or reception area to a larger room.

   “Who knows. Perhaps the Ark is still waiting in some antechamber for us to discover. Perhaps there's some vital bit of evidence which eludes us. Perhaps…”

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

2. The space immediately below the guard cells of a stoma.