Term of respect for a woman of the peerage without using her title."Her ladyship will be unable to attend tonight," he said, with a wink because he hadn't said why.
1877, Anna Sewell, Black Beauty Chapter 22http://en.wikisource.org/wiki/Black_Beauty/22York got down and said very respectfully, "I beg your pardon, my lady, but these horses have not been reined up for three years, and my lord said it would be safer to bring them to it by degrees; but if your ladyship pleases, I can take them up a little more."
(English & Commonwealth) Formal form of address for a lady judge (as opposed to the informal "judge")
