antechamber (n.)

c. 1200, "a room in a house," usually a private one, from Old French chambre "room, chamber, apartment" (11c.), from Late Latin camera "a chamber, room" (see camera).

The Old French word and the Middle English one also were used alone and in combinations to form words for "latrine, privy" from the notion of "bedroom utensil for containing urine." In anatomy, "enclosed space in a body," from late 14c. Of machinery, "artificial cavity," from 1769. Gunnery sense "part of the bore in which the charge is placed" is from 1620s. Meaning "legislative body" is from c. 1400, an extended sense from the chambers or rooms where an assembly meets. Chamber music (1765) traditionally was that meant to be performed in smaller spaces.

DA CAMERA: of the chamber, i. e. belonging to the chamber, suitable for the chamber, designed for the chamber,—a term applied to parlor or chamber music. [Godfrey Weber's General Music Teacher," Boston, 1842]