The Collaborative International Dictionary of English v.0.48:

Tribunal \Tri*bu"nal\, n. [L. tribunal, fr. tribunus a tribune
   who administered justice: cf. F. tribunal. See Tribune.]
   1. The seat of a judge; the bench on which a judge and his
      associates sit for administering justice.
      [1913 Webster]

   2. Hence, a court or forum; as, the House of Lords, in
      England, is the highest tribunal in the kingdom.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Tribunal \Tri`bu*nal"\, n. [Sp.]
   In villages of the Philippine Islands, a kind of townhall. At
   the tribunal the head men of the village met to transact
   business, prisoners were confined, and troops and travelers
   were often quartered.
   [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

tribunal
    n 1: an assembly (including one or more judges) to conduct
         judicial business [syn: court, tribunal, judicature]