A is a long-term female lover and companion who are not
married to her partner; the term is used especially when her partner is
married. The relationship generally is stable and at least semi-permanent;
however, the couple does not live together openly. Also the relationship is
usually, but not always, secret. There is an implication that a mistress may be
"kept" i.e., that the lover is paying for some of the woman's living
expenses. The word mistress was originally used as a neutral counterpart to
mister or master.
