Reardan is a variant of the name Anna, which is derived from the Greek name Anna, meaning gracious or merciful. In medieval times, the name Anna was popularized by Saint Anna, the mother of Jesus Christ. Reardan is also associated with the Old English word regn, meaning kingdom or realm, which may have been used to signify a connection to power or nobility. The name Reardan has been in use since the Middle Ages and is found in various forms throughout history, including Reanna, Reannah, and Reanne.