Black Oroogu is a language spoken by an unknown group of people on the Disc. It has no nouns, and only one adjective, which is obscene.
In The Colour of Magic, it is mentioned as one of many languages that Rincewind can speak. In fact, he attempts to speak in Black Oroogu to Twoflower, but does not succeed. (The only common language between Twoflower and Rincewind turns out to be the language of Trob).