From BiblePortal Wikipedia

Webster's Dictionary [1]

(1): ( n.) A married woman; a wife.

(2): ( n.) The old name of the jack at bowls.

(3): ( v. i.) To wait upon a mistress; to be courting.

(4): ( n.) A woman regarded with love and devotion; she who has command over one's heart; a beloved object; a sweetheart.

(5): ( n.) A woman filling the place, but without the rights, of a wife; a concubine; a loose woman with whom one consorts habitually.

(6): ( n.) A woman having power, authority, or ownership; a woman who exercises authority, is chief, etc.; the female head of a family, a school, etc.

(7): ( n.) A title of courtesy formerly prefixed to the name of a woman, married or unmarried, but now superseded by the contracted forms, Mrs., for a married, and Miss, for an unmarried, woman.

(8): ( n.) A woman well skilled in anything, or having the mastery over it.

King James Dictionary [2]

MIS'TRESS, n. L. magistra.

1. A woman who governs correlative to servant, slave, or subject.

My mistress here lies murdered in her bed.

2. The female head of a family. 3. That which governs a sovereign. Rome was mistress of the world. 4. One that commands, or has possession and sovereignty. The queen is mistress of the Indies. 5. A female who is well skilled in any thing as, she is mistress of arithmetic. 6. A woman teacher an instructress of a school. 7. A woman beloved and courted. 8. A woman in keeping for lewd purposes. 9. A term of contemptuous address.

MIS'TRESS, To wait upon a mistress to be courting.

International Standard Bible Encyclopedia [3]

mis´tres ( בּעלה , ba‛ălāh , גּברת , gebhereth ): Is the translation of ba‛ălāh , "lady," "owner" (  1 Kings 17:17;  Nahum 3:4 ); in  1 Samuel 28:7 , "a woman that hath a familiar spirit" is literally, "the mistress of a familiar spirit"; of gebhereth ( Genesis 16:4 ,  Genesis 16:8 ,  Genesis 16:9;  2 Kings 5:3;  Psalm 123:2;  Proverbs 30:23;  Isaiah 24:2 ); in  Isaiah 47:5 ,  Isaiah 47:7 , we have the King James Version and the English Revised Version "lady," the American Standard Revised Version "mistress."