Daemon Names

Names hold power in the Old World, especially in magical matters. Some say that everything in existence has a True Name, and to know it grants mastery over the object. Nowhere is this truer than with Daemons. To know a Daemon's True Name gives an individual a decided advantage in dealings with such creatures, aiding in controlling them. Because these Names are so potent, Daemons go to great lengths to protect their identities, including using aliases and titles called Use-Names. 1a

Use-Names
Use-Names are typically nonsense names, collections of evocative words the Daemon finds entertaining or suitable. In no way is the Daemon bound to just one Use-Name. In fact most Daemons have several, and they often, inexplicably, switch from one name to another. Examples include Red Flayer, Bloodspoor, Frothmaggot the Fury, and so on, so long as they reflect the nature of the Daemon.

True Names
True Names are nothing like Use-Names. They are alien and unpronounceable, giving even the most schooled scholars in the occult fits and starts as they try to work around the jumbles of letters. But often the research and struggle is worth it, for these names offer a mortal leverage when dealing with the Daemon.

Daemons do their best to keep their True Names hidden. They never reveal their names unless faced with utter annihilation, though almost all are willing to cough up the name of a weaker and less significant Daemon in exchange for freedom. Other avenues for finding True Names include grimoires and forbidden tomes. Some say that within the most blasphemous texts one can find the True Names of the Greater Daemons hidden within the words themselves. But such knowledge is rare and hard to acquire, and those who have it are loath to give it up.

Source
pg. 238
 * Warhammer Fantasy RPG 2nd ED -- Tome of Corruption

pg. 239