The Collaborative International Dictionary of English v.0.48:

Justiciary \Jus*ti"ci*a*ry\, n. [Cf. LL. justitiarius, F.
   justicier. See Justice.] (Old Eng. Law)
   An old name for the judges of the higher English courts.
   [1913 Webster]

   Note: The chief justiciary, or justiciar, in early English
         history, was not only the chief justice of the kingdom,
         but also ex officio regent in the king's absence.
         [1913 Webster]

   Court of justiciary (Scots Law), the supreme criminal
      court, having jurisdiction over the whole of Scotland.
      Justico

WordNet (r) 3.0 (2006):

justiciary
    n 1: formerly a high judicial officer [syn: justiciar,
         justiciary]
    2: the jurisdiction of a justiciar

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

JUSTICIARY, officer. Another name for a judge. In Latin, he was called
justiciarius, and in French, justicier. Not used. Bac. Ab. Courts and their
Jurisdiction, A.