The Collaborative International Dictionary of English v.0.48:

Deemster \Deem"ster\ (d[=e]m"st[~e]r), n. [Deem + -ster; i. e.,
   doomster. Cf. Dempster.]
   A judge in the Isle of Man who decides controversies without
   process. --Cowell.
   [1913 Webster]