Mistress (noun)

1. A woman in a position of authority or control.
2. A woman who is having an extramarital affair with a married man.
3. A woman who is skilled or knowledgeable in a particular subject or activity.

Origin:

From old english maegestre (female teacher or head of household).

Examples:

1. The mistress of the house welcomed us warmly and showed us around.
2. The king's mistress held great influence over his decisions.
3. The scandalous affair between the politician and his mistress was front-page news.
4. The chef is a mistress of French cuisine, having trained in Paris for many years.
5. The singer is a mistress of many musical styles, from jazz to opera.