Bauglir

The origins of this name are never explained in detail, but the fact that it is Sindarin in form suggests that Morgoth must have acquired it after his return to Middle-earth.

'The Constrainer' is Christopher Tolkien's preferred interpretation of Bauglir, and this is borne out by his father's notes in The Etymologies (in volume 5 of The History of Middle-earth) where a bauglir is a general Elvish word for any tyrant or oppressive ruler. However, this is not the only possible translation, and in fact - as originally conceived - it seems that Bauglir was intended as a title meaning 'the Terrible'.