mid-13c., etymologically "person who manages a chamber or chambers," but by the time the word reached English it had evolved to describe an important royal officer of various duties, such as "one who attends a king or person of high rank in his or her private chamber," and especially "keeper of the treasure-chamber;" from Old French chamberlenc "chamberlain, steward, treasurer" (Modern French chambellan), from a Germanic source (perhaps Frankish *kamerling; compare Old High German chamarling, German Kämmerling), from Latin camera "chamber, room" (see camera) + Germanic diminutive suffix -ling. As "chief financial officer of the king's household" from mid-15c.
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]