In the last few years an Internet meme has been going around that "poison" is a substance that has a negative effect when ingested, while "venom" has to be injected. Ergo, "poisonous snakes" should really be "venomous snakes" etc. I have also heard people repeat this definition both in-person and online.
However, this doesn't align with my intuition, nor can I find a source to substantiate this distinction. From my research, "poison" derives from the same root as "potion", so there is some reason there for it to mean exclusively a substance that is eaten. But one can very easily make the argument it means a liquid that needs to enter the body via some means to have an effect. On the other hand, "venom" is from "venenum", which itself shares meaning with "poison". In French for example you would use either "venimeux" or "toxique", but there's no word for "poisonous" with a root derived from "poison". Same for Italian. You would definitely describe a "poisonous beverage" as "venimeux".
From this it seems there is no real historical justification for the contemporary usage I see repeated around the Internet. The modern descendants of Latin themselves don't make this distinction and use "venom"-derived words for "poison". I know a bit of Russian too and there is just one word for both "venom" and "poison" when speaking of substances and a completely different word for the metaphorical meaning of speaking negatively with passion (i.e. to spit venom).
Can anyone point to an actual historical reason for the modern definition of "poison has to be eaten, while venom has to be injected"? Or is this a new development in English?