Languages constructed by J. R. R. Tolkien
Khuzdûl is the language of the Dwarves. The dwarves keep much of what they do a secret, and they also do this with their language. Because of this, only a few place-names and phrases are known from Khuzdûl. Dwarves have never told other (non-dwarven) people their Khuzdûl names. Instead, they use other names when talking to the other peoples of Middle-earth. The dwarven "nicknames" that appear in the books are  all taken from Norse mythology.