Title for a lady

Answer 1

If you are using "lady" meaning a person of feminine gender, you may use:

Missus (Mrs.) used when addressing a married woman.

Miss used when addressing an unmarried woman.

Ms. used when addressing of indeterminate marital status.

Mistress, is an antiquated term for a woman who runs her husband's (or sometimes father's) household - these days it has other meanings.

Madame, is a word borrowed from the French and used when addressing a woman of indeterminate marital status - most frequently by someone of lesser station.

Ma'am, is commonly used in the southern United States when addressing any woman.

If the woman in question holds a doctorate she is addressed as Doctor Whomever

A woman Judge is Your Honour.

A woman Mayor or other personage of political title is referred to as The Honourable, whomever.

A woman of the cloth is address as Story, Reverend, Sister, Reverend Mother, Rabbi, etc.

A woman in any branch of the Armed Forces is addressed by her rank or simply Ma'am.

If you are referring to a woman who is married to a Lord or gentleman then the term Lady is used, often with her husband's (and these days her own) titled lands. ie. Alice, Lady Belfor.

There are related links below to further muddy the waters of etiquette.

Answer 2

Miss, or Ms. if she prefers not to communicate her marital status.