The Collaborative International Dictionary of English v.0.48:

Antechamber \An"te*cham`ber\, n. [Cf. F. antichambre.]
   1. A chamber or apartment before the chief apartment and
      leading into it, in which persons wait for audience; an
      outer chamber. See Lobby.
      [1913 Webster]

   2. A space viewed as the outer chamber or the entrance to an
      interior part.
      [1913 Webster]

            The mouth, the antechamber to the digestive canal.
                                                  --Todd &
                                                  Bowman.
      [1913 Webster]

WordNet (r) 3.0 (2006):

antechamber
    n 1: a large entrance or reception room or area [syn:
         anteroom, antechamber, entrance hall, hall,
         foyer, lobby, vestibule]