The news that Jack Vance has passed away reminded me of an unsolved lexicographical mystery which now seems further than ever from resolution: the source of the word libram for a grimoire or more generically a book, which has turned up in various works of fantasy and for which Vance is thought to be the earliest (and the original?) source.

I don’t know how it ought to be pronounced (Lee-brum and Lie-brum seem equally plausible). It isn’t even good Latin; assuming that it must be from liber ‘book’, ‘libram’ is not a valid declination.¹ It is the accusative singular form of the feminine noun libra ‘balance, scales’, but I presume that’s not what we’re after! And the less said about the ‘Libram Libris Bestiis Chaotis’ from the Warhammer Fantasy Encyclopedia rulebook, the better!
From the Dungeon to the Dictionary

Some searching eyes traced the word as far as Vance, but as far as I know nobody asked him about it while it was still possible. Now it never will be, and unless some earlier source is found we’ll never know whether libram was a mistake, a deliberate coinage or a word Vance took from somewhere else.

1. Jack Rawlins, in Demon Prince: The Dissonant Worlds of Jack Vance (p. 54), appears not to know this: he thinks Vance took a Latin word and appended ‘an -m suffix that brings associations of learning, age, and authority by its similarity to in words [sic] like sanctum, compendium, theorum [sic], and vellum (parchment). A libram, then, has the connotation of being an old, authoritative collection of wisdom on parchment.’ I find this reasoning a touch ‘ad hokum’. ↩