1. Used as a courtesy title before the surname, full name, or professional title of a man, usually written in its abbreviated form: Mr. Jones; Mr. Secretary.
2. Used as the official term of address for certain U.S. military personnel, such as warrant officers.
3. mister Informal. Used as a form of address for a man: Watch your step, mister.
4. Informal. Used as a term of reference by a woman of her husband.

[Alteration of MASTER.]

The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.