Source : Webster's Revised Unabridged Dictionary (1913)

Diocesan \Di*oc"e*san\ (?; 277), a. [LL. dioecesanus: cf. F.
   dioc['e]sain.]
   Of or pertaining to a diocese; as, diocesan missions.

Diocesan \Di*oc"e*san\, n.
   1. A bishop, viewed in relation to his diocese; as, the
      diocesan of New York.

   2. pl. The clergy or the people of a diocese. --Strype.

Source : WordNet®

diocesan
     adj : belonging to or governing a diocese
     n : a bishop having jurisdiction over a diocese