http://www.wordorigins.org

Lord

This word for master derives from the Old English hláford or literally bread (loaf)-ward.
Originally, it is a reference to the head of a household; servants in the house would be
entitled to be fed by the master. The general sense of master, as opposed to the specific
sense of a provider of bread, is well established by c. 950.

This site didn't give etymology of "lady" which comes from roots about kneading bread.