Wiktionary
n. 1 A literary collection of legends, particularly those detailing the life of a saint 2 (context literature English) The collected high fantasy writings of J. R. R. (w: Tolkien) related to the fictional realm of (w: Middle-earth) and the universe in which it is set
Usage examples of "legendarium".
This legendarium ends with a vision of the end of the world, its breaking and remaking, and the recovery of the Silmarilli and the 'light before the Sun' – after a final battle which owes, I suppose, more to the Norse vision of Ragnarök than to anything else, though it is not much like it.
But the beginning of the legendarium, of which the Trilogy is pan (the conclusion), was in an attempt to reorganize some of the Kalevala, especially the tale of Kullervo the hapless, into a form of my own.