Apparently from the Proto-Germanic elements *austrą "east" (Old High German *ōst, Modern German Ost or Osten) and *dagaz "day" (Old High German tag, Modern German Tag).Hypothetical cognates of this name include Old Norse *Austrdagr (cf. DAGR) and Old English *Ēastdæġ (cf. EASTMUND, LEOFDÆG).