The Collaborative International Dictionary of English v.0.48:

Dempster \Demp"ster\ (?; 215), Demster \Dem"ster\, n. [See
   Deemster.]
   1. A deemster.
      [1913 Webster]

   2. (O. Scots Law) An officer whose duty it was to announce
      the doom or sentence pronounced by the court.
      [1913 Webster]