Black Speech and Ringwraiths

[doug*platypus]

To call them anything but Nazgûl is euphemistic. Nazgûl is the most evil and most applicable term for them. Anyone wishing in a certain situation or in general to make them appear utterly evil does not hesitate to use the word. Only someone who has an enormous fear of them, like Gollum or the hobbits, will not dare to speak their proper name. Even the word Mordor has dark connotations, and is not used lightly, at least not in the Shire.

So the reason that the word Nazgûl is used is the same reason that Gandalf chose to use the Black Speech at Rivendell - for effect.