The Collaborative International Dictionary of English v.0.48:

Star chamber \Star" cham`ber\, Star-chamber
\Star"-cham`ber\(st[aum]r"ch[=a]m`b[~e]r), n. [So called (as
   conjectured by Blackstone) from being held in a room at the
   Exchequer where the chests containing certain Jewish
   contracts and obligations called starrs (from the Heb.
   shetar, pron. shtar) were kept; or from the stars with which
   the ceiling is supposed to have been decorated.]
   1. (Eng. Hist.) An ancient high court exercising jurisdiction
      in certain cases, mainly criminal, which sat without the
      intervention of a jury. It consisted of the king's
      council, or of the privy council only with the addition of
      certain judges. It could proceed on mere rumor or examine
      witnesses; it could apply torture. It was abolished by the
      Long Parliament in 1641. --Encyc. Brit.
      [1913 Webster]

   2. Hence: (Metaphorical) Any court, committee, or other
      tribunal which exercises arbitrary and unaccountable
      power, or uses unfair or illegal methods, in investigation
      or judgment of persons.
      [PJC]

WordNet (r) 3.0 (2006):

Star Chamber
    n 1: a former English court that became notorious for its
         arbitrary methods and severe punishments

Bouvier's Law Dictionary, Revised 6th Ed (1856):

STAR CHAMBER, Eng. law. A court which formerly had great jurisdiction and
power, but which was abolished by stat. 16,  C. I., c. 10, on account of its
usurpations and great unpopularity. It consisted of several of the lords
spiritual and temporal, being privy counsellors, together with two judges of
the courts of common law, without the intervention of a jury. Their legal
jurisdiction extended over riots, perjuries, misbehaviour of public
officers, and other great misdemeanors. The judges afterwards assumed
powers, and stretched those they possessed to the utmost bounds of legality.
4 Bl. Com. 264.