a: any of various titled women in Great Britain —used as the customary title of (1) a marchioness, countess, viscountess, or baroness or (2) the wife of a knight, baronet, member of the peerage, or one having the courtesy title of lord and used as a courtesy title for the daughter of a duke, marquess, or earl
b: a woman who is a member of an order of knighthood — compare dame
: a British noblewoman —used as a title <Lady Jane Grey>
Word History of LADY
Lady was actually formed as a compound word, though its nature has been completely disguised by centuries of sound change. The Old English ancestor of lady was hlǣfdige, “female head of the household.” This compound is made up of hlāf, “loaf, bread,” and -dige, which is thought to mean “kneader,” and is akin to Old English dāg, “dough.” Why the “kneader of dough” was thought to be the most important woman in the household we are not quite sure.