An Honorarium is a compendium of titles, ranks, and honors bestowed upon the Pendragon of Slayer Dragons. Each Pendragon's honorarium would be composed during his life and completed for publication upon his death. Typically, authors would try to fit the entire honorarium in a single volume, however this was not always possible.
Beginning with Eieber, it became customary to, whenever the Pendragon visited the lands of a friendly nation, either belonging to the Alliance or not, for that nation to bestow upon him so form of title or honor.
The custom even extended down to the local level. If the Pendragon stopped in your town you might give some sort of title or make him an "honorary" part of some organization.
The concept evolved out of the Mage Wars, when various governments would place troops under Eieber's command. In order to ensure those soldier's loyalties, Eieber would be given an "honorary" command-rank in that nation's military. Upon his death, as scholars set about gathering all of the ranks and titles he had received, the term "honorarium" was coined.
Throughout the ages, Honoraria were kept for each Pendragon and released shortly after their deaths. These would later become invaluable resources for scholars and historians as they contained bountiful information about long lost cultures and lands.