The Collaborative International Dictionary of English v.0.48:

Decanal \Dec"a*nal\ (?; 277), a. [Cf. F. d['e]canal. See
   Dean.]
   Pertaining to a dean or deanery.
   [1913 Webster]

         His rectorial as well as decanal residence. --Churton.
   [1913 Webster]

   Decanal side, the side of the choir on which the dean's
      tall is placed.

   Decanal stall, the stall allotted to the dean in the choir,
      on the right or south side of the chancel. --Shipley.
      [1913 Webster]