Miyasundokoro (御息所)

Miyasundokoro or Miyasudokoro
The Emperor's rest area

A lady serving at the Imperial Court who was lower rank than the Emperess
A generic name of serving ladies at the Imperial Court who were favourites with the Emperor, including nyogo (a high-ranking lady in the court who was a consort of the emperor), koi (a lady in waiting in the court) and other lower rank ladies

Imperial Princess

Miyasundokoro was…

Miyasundokoro literally meant the Emperor's rest area. Then gradually, it came to mean a lady serving at the Imperial Court who served at the Emperor's bedroom. In one theory, it means nyogo or koi who was a mother of Prince and Princess, but it is generally accepted that it was the name of ladies at the inner palace who were loved by the Emperor, such as nyogo and koi except for serving ladies. It sometimes meant Naishi no Tsukasa (female palace attendants), and there was a precedent that the Emperor's mother was called Grand Miyasundokoro. Later, the meaning of Miyasundokoro which was nyogo and koi faded out, and then Miyasundokoro became the name for crown princess and Imperial Princess.

[Original Japanese]