The Collaborative International Dictionary of English v.0.48:

Diocese \Di"o*cese\, n.; pl. Dioceses. [OE. diocise, OF.
   diocise, F. dioc['e]se, L. dioecesis, fr. Gr. ? housekeeping,
   administration, a province, a diocese, fr. ? to keep house,
   manage; dia` through + ? to manage a household, ? a house.
   See Economy.] (Eccl.)
   The circuit or extent of a bishop's jurisdiction; the
   district in which a bishop exercises his ecclesiastical
   authority. [Frequently, but improperly, spelt diocess.]
   [1913 Webster]

WordNet (r) 3.0 (2006):

diocese
    n 1: the territorial jurisdiction of a bishop [syn: diocese,
         bishopric, episcopate]