'To be one's own mistress' definitions:

Definition of 'To be one's own mistress'

From: GCIDE

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. [1913 Webster]
The late queen's gentlewoman! a knight's daughter! To be her mistress' mistress! --Shak. [1913 Webster]
2. A woman well skilled in anything, or having the mastery over it. [1913 Webster]
A letter desires all young wives to make themselves mistresses of Wingate's Arithmetic. --Addison. [1913 Webster]
3. A woman regarded with love and devotion; she who has command over one's heart; a beloved object; a sweetheart. [Poetic] --Clarendon. [1913 Webster]
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. [1913 Webster +PJC]
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 A title of courtesy formerly prefixed to the name of a woman, married or unmarried, but now superseded by the contracted forms, Mrs., for a married, and Miss, for an unmarried, woman. [1913 Webster]
Now Mistress Gilpin (careful soul). --Cowper. [1913 Webster]
6. A married woman; a wife. [Scot.] [1913 Webster]
Several of the neighboring mistresses had assembled to witness the event of this memorable evening. --Sir W. Scott. [1913 Webster]
7. The old name of the jack at bowls. --Beau. & Fl. [1913 Webster]
To be one's own mistress, to be exempt from control by another person. [1913 Webster]