mayor

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

• noun The head of government of a city, town, borough, or municipal corporation.

from The Century Dictionary.

• noun The principal officer of a municipality; the chief magistrate of a city or borough.

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

• noun The chief magistrate of a city or borough; the chief administrative officer of a municipal corporation. In some American cities there is a city court of which the major is chief judge. The post is usually elective, its holder chosen by the electorate of the entire city.

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

• noun The leader of a city, or a municipality, sometimes just a figurehead and sometimes a powerful position. In some countries, the mayor is elected by the citizens or by the city council.
• noun historical The steward of some royal courts, particularly in early Medieval France

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

• noun the head of a city government