What is the archaic connotation of word mistress as used in Shakespeare s Sonnet 130?

The word "mistress" in Shakespeare's Sonnet 130 does not carry any archaic connotation. In the context of the sonnet, it simply means "female lover" or "sweetheart." There is no suggestion of the more modern meaning of "dominatrix" or "female tyrant."

Here is the relevant passage from Sonnet 130:

My mistress' eyes are nothing like the sun;

Coral far more red than her lips' red;

If snow be bright, why then her breasts are dun;

If fur be soft, bristles grow on her head.

It is clear from this passage that the speaker is comparing his mistress to various natural objects, and finding her wanting in each case. Her eyes are not as bright as the sun, her lips are not as red as coral, her breasts are not as white as snow, and her hair is not as soft as fur. However, this does not mean that the speaker does not love her. In fact, he concludes the sonnet by saying, "And yet, by heaven, I think lovers are rare / Who think their loves as true as mine." Clearly, the speaker's mistress is special to him, even if she does not conform to conventional standards of beauty.