diocese

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The district or churches under the jurisdiction of a bishop; a bishopric.

from The Century Dictionary.

• noun A district or division of a country; a province: now obsolete except when used with reference to Norway, an episcopal diocese (stift) of which, as a geographical division of the country, is sometimes regarded as a province, though it has no provincial civil administration.
• noun Under the Roman empire after Diocletian and Constantine, a subdivision of a prefecture, comprising a number of provinces; hence, a corresponding extent of territory as an ecclesiastical division, including a number of provinces or eparchies, each province again containing a number of parœciæ, which themselves finally came to be called dioceses in the following (modern) sense.
• noun The district, with its population, falling under the pastoral care of a bishop.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Eccl.) The circuit or extent of a bishop's jurisdiction; the district in which a bishop exercises his ecclesiastical authority.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun Administrative division of the later Roman Empire, starting with the Tetrarchy.
• noun religion Region administered by a bishop.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun the territorial jurisdiction of a bishop