Well, one of my friends is quite fond of Latin, so this is what she has to offer:
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If you want "book of poisons", one option is "Liber Virorum". Virus, in Latin, is a poison (or slime, or a bad smell, or a salty taste), but of course we associate the English word, "virus" with disease---so you'd be referring to both topics (poison and disease) in one. Other possibilities are "Liber Toxicorum" and "Liber Venenorum". If you want a "book of harmful things", you might call it "Liber Rerum Noxiorum", or "Liber Noxiorum" for short. Whatever you choose, you want nominative singular for the book, and genitive plural for the bad stuff.
You were asking after a more impressive word for book. Why not call it a tract? Something along the lines of "Tractatus de Viris", "Tractatus de Toxicis, or "Tractatus de Rebus Noxiis". "Tractatus" takes de + ablative plural. Another common title-beginning for mediaeval treatises is "Speculum" (+ genitive), which is a "mirror of [whatever the topic is]".