The Collaborative International Dictionary of English v.0.48:

Chamber \Cham"ber\, n. [F. chambre, fr. L. camera vault, arched
   roof, in LL. chamber, fr. Gr. ? anything with a vaulted roof
   or arched covering; cf. Skr. kmar to be crooked. Cf.
   Camber, Camera, Comrade.]
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   1. A retired room, esp. an upper room used for sleeping; a
      bedroom; as, the house had four chambers.
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   2. pl. Apartments in a lodging house. "A bachelor's life in
      chambers." --Thackeray.
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   3. A hall, as where a king gives audience, or a deliberative
      body or assembly meets; as, presence chamber; senate
      chamber.
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   4. A legislative or judicial body; an assembly; a society or
      association; as, the Chamber of Deputies; the Chamber of
      Commerce.
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   5. A compartment or cell; an inclosed space or cavity; as,
      the chamber of a canal lock; the chamber of a furnace; the
      chamber of the eye.
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   6. pl. (Law.) A room or rooms where a lawyer transacts
      business; a room or rooms where a judge transacts such
      official business as may be done out of court.
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   7. A chamber pot. [Colloq.]
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   8. (Mil.)
      (a) That part of the bore of a piece of ordnance which
          holds the charge, esp. when of different diameter from
          the rest of the bore; -- formerly, in guns, made
          smaller than the bore, but now larger, esp. in
          breech-loading guns.
      (b) A cavity in a mine, usually of a cubical form, to
          contain the powder.
      (c) A short piece of ordnance or cannon, which stood on
          its breech, without any carriage, formerly used
          chiefly for rejoicings and theatrical cannonades.
          [1913 Webster]

   Air chamber. See Air chamber, in the Vocabulary.

   Chamber of commerce, a board or association to protect the
      interests of commerce, chosen from among the merchants and
      traders of a city.

   Chamber council, a secret council. --Shak.

   Chamber counsel or Chamber counselor, a counselor who
      gives his opinion in private, or at his chambers, but does
      not advocate causes in court.

   Chamber fellow, a chamber companion; a roommate; a chum.

   Chamber hangings, tapestry or hangings for a chamber.

   Chamber lye, urine. --Shak.

   Chamber music, vocal or instrumental music adapted to
      performance in a chamber or small apartment or audience
      room, instead of a theater, concert hall, or church.

   Chamber practice (Law.), the practice of counselors at law,
      who give their opinions in private, but do not appear in
      court.

   To sit at chambers, to do business in chambers, as a judge.
      [1913 Webster]

WordNet (r) 3.0 (2006):

chamber music
    n 1: serious music performed by a small group of musicians

Moby Thesaurus II by Grady Ward, 1.0:

34 Moby Thesaurus words for "chamber music":
   Nachtmusik, absolute music, adaptation, air varie, aleatory,
   aleatory music, arrangement, chamber orchestra, composition,
   descant, electronic music, etude, exercise, harmonization,
   incidental music, instrumental music, invention, nocturne, opus,
   orchestration, piece, production, program music, ricercar, score,
   sonata, sonatina, string orchestra, string quartet, study,
   theme and variations, trio, variation, work