"Mor" may derive from an Indo-European root connoting terror, monstrousness cognate with the Old English "maere" (which survives in the modern English word "nightmare") and the Scandinavian "mara" and the Old East Slavic "mara" ("nightmare"); while "rígan" translates as "queen".This etymological sequence can be reconstructed in the Proto-Celtic language as *"Moro-rīganī-s".