chamber
An enclosed room or space used for a special purpose.
A chamber is an enclosed space or room, especially one designed for a specific purpose. A judge might meet with lawyers in her chambers (her private office), while a diver explores an underwater chamber formed by ancient rocks. The human heart has four chambers that pump blood through your body.
In government, a chamber means one part of a legislature. The United States Congress has two chambers: the Senate and the House of Representatives. Each chamber votes on laws separately, and both must agree before a bill becomes law. England's Parliament also has two chambers: the House of Commons and the House of Lords.
You might also encounter chamber music, which means classical music written for a small group of instruments, originally meant to be played in a room (a chamber) rather than a large concert hall. A string quartet playing in someone's living room is performing chamber music.