ETYM Old Eng. maistress, Old Fren. maistresse, French maîtresse, Late Lat. magistrissa, for Latin magistra, fem. of magister. Related to Master, Mister, Miss a young woman.
1. A woman master who directs the work of others.
2. A woman who has an ongoing extramarital sexual relationship with a man; SYN. kept woman, fancy woman.