Lewis & Short

Thyrsăgĕtae, Thyssăgĕtae, or Thussăgĕtae, ārum, m., a people of Asiatic Sarmatia, on the Wolga, Val. Fl. 6, 140; Mel. 1, 19, 19; Plin. 4, 12, 26, § 88.
Sing.: Thyrsagĕtes, ae, m., Val. Fl. 6, 135.