Madam

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

• noun Used formerly as a courtesy title before a woman's given name but now used only before a surname or title indicating rank or office.
• noun Used as a salutation in a letter.
• noun Used as a form of polite address for a woman.
• noun The mistress of a household.
• noun A woman who manages a brothel.

from The Century Dictionary.

• noun My lady; lady: originally a formal term of address to a lady (a woman of rank or authority, or the mistress of a household); now a conventional term of address to women of any degree, but chiefly to married and matronly women.
• noun A title used to designate women under the rank of Lady, but moving in respectable society; prefixed to a surname, equivalent to Mrs. Compare mistress.
• noun See the quotation. The use mentioned is not uncommon in all parts of the United States.
• noun A lady; a woman of fashion or pretension often used with a suggestion of disparagement: as, a conceited madam; city madams.
• To address as madam.

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

• noun A gentlewoman; -- an appellation or courteous form of address given to a lady, especially an elderly or a married lady; -- much used in the address, at the beginning of a letter, to a woman. The corresponding word in addressing a man is Sir; often abbreviated ma'am when used as a term of address.
• noun The woman who is in charge of a household.
• noun The woman who is in charge of a brothel.

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

• noun a woman who runs a house of prostitution
• noun a woman of refinement