Nyobo (a court lady) (女房)
Nyobo was a female servant who did domestic matters for people in the Imperial court or a distinguished person in aristocratic circles from the Heian period to around the Edo period. The name of nyobo was derived from the chamber which was assigned to them in the Imperial court or the residence of the court noble that they attended. They were high-ranking servants who took care of solely domestic chores of their master. Sometimes nyobo played roles as a wet nurse, a private tutor for an infant or a girl master, or a clandestine secretary for a boy master. If her master was male, she often became his concubine; on the other hand, if her master was female, she had relationships with men who visited her master. On the whole, she retired from her service when she got married. Among the nyobo working in the Imperial palace, a court lady who served the Emperor was called 'Ue no nyobo,' and she was distinguished from the nyobo privately serving the Empress (or her family) in kokyu (Empress's residence).
In the society after the mid-Heian period, girls from the middle-ranking families such as Zuryo (the head of the provincial governors) often entered the service, therefore they were intelligent. They had a big influence on the Kokufu Bunka (Japan's original national culture) such as usage of the hiragana syllabary. There were many nyobo who were good at waka poetry and Japanese literature, so the literary works that were created from the Heian period to the Kamakura period by the authors belonging to this class are specifically called nyobo bungaku (literature by nyobo).
Diversion of the word
In modern Japan, the word nyobo mentioned above is used as another name for a wife. Moreover, it sometimes indicates a partner in business. For example, a catcher (toward a pitcher) in baseball games, and so on.
According to the dialect in the Unpaku (Izumo, Hoki) provinces, a woman is called 'nyoba,' which seems to have the same origin.