or On'yo-ryo. The Bureau of Yin and Yang established in the ritsuryo system to observe, record and divine the movements of the heavens as well as other elements of onmyodo. The imperial court employed onmyo-shi or on'yoshi, 'Masters of Yin and Yang', Taoist ritual specialists, from the ritsuryo period up to the Meiji restoration.
A Popular Dictionary of Shinto. Brian Bocking.