1st First Lady, Dolly MadisonMartha Washington was referred to as Lady Washington, in the early 19th century, while terms like Mrs. President and Presidentress were used until 1849, when, at the funeral of Dolley Madison, the term First Lady was applied to describe the recently departed president's wife.
Known as the first First Lady of the land, Dolley Madison, served as official hostess for Thomas Jefferson (US president from 1801-1809) and later her husband, James Madison (US president from 1809-1817).
The first mention of First Lady is in British correspondent William Russell's My Diary North and South (1863): "The gentlemen...has some charming little pieces of gossip about the first Lady in the Land (then Mary Todd Lincoln)."
The term is also used, usually uncapitalized, for a prominent woman in any profession, as in "She's the first lady of the American theater."
Jacqueline Kennedy is the only First Lady who didn't want to be called First Lady (so far, that is). She said it sounded like the name of a saddle horse.
Jackie K.