What is "rethra"

Rethra (also known as Radagoszcz, Radegost, Radigast, Redigast, Radgosc and other forms) was, in the 10th to the 12th centuries, the main town and political center of the Slavic Redarians, one of the four major Lutician tribes, located most likely in present-day Mecklenburg. It was also a major worship center, devoted to the cult of the Slavic deity Radegast- Swarożyc.