Sind.: probably ú + dûn ... not west, also meaning hell
1) The source of the dark flame of the Balrogs, the hell, probably Utumno (c.f. Flame of Udûn).
2) The Sindarin name for Utumno, Melkor's first fortress in Arda.
2) A circular plain in northwest Mordor, between the Morannon and Isenmouthe.