From the Tang and Song Dynasties onwards, sisters of the reigning emperor were given the title of Chokoshu (roughly, elder Koshu), and aunts and Koshu ladies in the previous reigns were given the title of Daichokoshu (roughly, great elder koshu, e.g., 秦魯国賢穆明懿大長公主), to distinguish from daughters of the reigning emperor, with better treatment than the daughters.
唐宋以後、今上の姉妹は長公主（ちょうこうしゅ）、今上の伯叔母や数代前の公主は大長公主（だいちょうこうしゅ）（例：秦魯国賢穆明懿大長公主）と呼んで今上の娘と区別し、受けた待遇も公主より上だった。