The oposite? In gender specific terms a baron is the masculine noun. A female with such a title would be a baroness. With this ambiguous question, I'll provide another answer incase you were mistaken with your spelling: The opposite of barren is fertile.
Baron is male, and Baroness is female.
The title for a male is duke; the title for a female (opposite by gender) is duchess.duchess
The term servant is not usually gender specific and is a universal title. To make it gender specific for female use maid.
Marquess or Marchioness
The opposite gender of lady is gentleman.The corresponding male honorary title is "lord" (the wife of a lord is also a lady).
The title for a woman (or the wife of a Lord) would be "Lady."
Baron .
opposite of Knight
The feminine form of the word baron is baroness. A baron is a lower level noble or aristocrat that that owns land.
A baron is male and a baroness is female.
There is no such title as the Baron of Avon. However, there is the title Earl of Avon.