Definition from Wiktionary, the free dictionary
Proper noun 
- (slang, US) Eye dialect spelling of His Honor, the mayor, especially of a large city.
- 1930, John Bright, Hizzoner Big Bill Thompson: An Idyll of Chicago, [book title].
- 1991, Max M. Kampelman, Entering New Worlds: The Memoirs of a Private Man in Public Life, page 56:
- Minnesota: Meet Hizzoner the Mayor... Canon... would go through an elaborate bowing-and-scraping routine as he addressed Hizzoner the Mayor.
- 2002, James Gill, For James and Gillian: Jim Gill's New York, page 121:
- In 1989, they wrote a book, entitled His Eminence and Hizzoner, in which they set forth their differences in amicable fashion.
Usage notes 
Cities in which the mayor is often called "Hizzoner" include Chicago, Las Vegas, Los Angeles, Newark, New Orleans, and New York City. The term can, but not always, connote a sense of "hardball" common to American urban politics.