Demonylogie Malyfycorum of Henchanse thee Unsatyfactory
Mentioned in Equal Rites, this is a book that Esk tries to read, until Simon gently takes it away from her, explaining why it's a bad idea to read books of magic unprepared (viz, they sometimes eat you), as in the example he gives of the Necrotelecomnicon, which had a lot more pages, each adorned with something that even Esk was unprepared to hear about after an erstwhile wizard read it unpreparedly and let his mind wander...
The Roundworld book from 1486, the Malleus Maleficarum means The Hammer of Witches, and was written to a) prove that witches exist and help out doing the Devil's work and b) how to prosecute and punish them.
The original title is in the feminine, alluding to the idea that it was women who were the evil-doers. Otherwise, it would be the Malleus Maleficorum (the masculine form of the Latin noun maleficus or malefica, 'witch'), which would mean The Hammer of (Male) Witches (Warlocks).
And a demonology is a list of demons and their names and properties.
So this title, Malyfycorum presumably refers to a book about the list of demons that male witches aid, and how to stop 'em doing it (i.e. mentioning them to the very disapproving Granny Weatherwax).