Some people devour books. Some books devour people.
And now, this is true for your fantasy OSR games, too!
A Devouring Tome is a hand written folio or manuscript whose topic centers on the occult and arcane and often is a mage´s grimoire. For a Devouring Tome is a book that has become possessed by an evil entity that spreads forbidden knowledge but claims the minds that seek it.
Reading in a Devouring Tome can reveal practices of the forbidden arts, the names of demons and their ilk, formula for elixirs and potions, powerful spells or wisdom of creatures, lands and artifacts of myth. But to study such a treatise is to invite doom.
I once wrote it for DarkHeresy, re-hashed it for Chthonian Highways and now provide it as a freebee for fantasy OSR games. The rules have been slightly changed to better fit the possible target system/s, but the core of the evil is still the same.