From 定 (sada) meaning "certain, true, definite, sure," also used as 貞, referring to chastity and virtue.Though it has had some level of usage as a feminine name in the Edo period (1603-1868) and, more commonly, in the Meiji and Taishō periods (1868-1912, 1912-1926) with some masculine usage in the latter two, since after WWII, it is very rarely used.