From The Collaborative International Dictionary of English v.0.48:
mayor \may"or\, n. [OE. maire, F. maire, fr. L. major greater,
higher, nobler, compar. of magnus great; cf. Sp. mayor. See
Major, and cf. Merino.]
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.
[1913 Webster]