What is "to be one's own mistress"

Mistress \Mis"tress\, n. [OE. maistress, OF. maistresse, F. ma[^i]tresse, LL. magistrissa, for L. magistra, fem. of magister. See Master, Mister, and cf. Miss a young woman.]

1. A woman having power, authority, or ownership; a woman who exercises authority, is chief, etc.; the female head of a family, a school, etc.

   The late queen's gentlewoman! a knight's daughter! To be her mistress' mistress!
   --Shak.

2. A woman well skilled in anything, or having the mastery over it.

   A letter desires all young wives to make themselves mistresses of Wingate's Arithmetic.
   --Addison.

3. A woman regarded with love and devotion; she who has command over one's heart; a beloved object; a sweetheart. [Poetic]
   --Clarendon.

4. A woman filling the place, but without the rights, of a wife; a woman having an ongoing usually exclusive sexual relationship with a man, who may provide her with financial support in return; a concubine; a loose woman with whom one consorts habitually; as, both his wife and his mistress attended his funeral.
   --Spectator.

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 A title of courtesy formerly prefixed to the name of a woman, married or unmarried, but now superseded by the contracted forms, Mrs., for a married, and Miss, for an unmarried, woman.

   Now Mistress Gilpin (careful soul).
   --Cowper.

6. A married woman; a wife. [Scot.]

   Several of the neighboring mistresses had assembled to witness the event of this memorable evening.
   --Sir W. Scott.

7. The old name of the jack at bowls.
   --Beau. & Fl.

   To be one's own mistress, to be exempt from control by another person.