The Oxford Thesaurus An A-Z Dictionary of Synonyms - mistressn.

1) lover, girlfriend, live-in lover, kept woman, concubine, inamorata, paramour, Literary odalisque, Archaic doxy, Colloq US alternative other, POSSLQ (= 'Person of the Opposite Sex Sharing Living Quarters') : She was the mistress of a leading politician. 2) schoolmistress, instructress, governess; headmistress: She had a rewarding career as a mistress in a girls' school in Lancashire.