What is the difference between “venom” and “poison”? Both in usage and in meaning.
Poison is contextual and can be an artificial or natural material — different materials can be poisons to different organisms in different doses and/or when misused. Further, poison usually denotes potential lethality.
Venom is a material created and used by an organism to aid in defense and/or hunting. Venoms are not necessarily fatal — many stun, sting, or disable. Venom is venom regardless of context, and can also be poison in some contexts.
Both words are used heavily in metaphor. Poison is often used to describe something that corrupts, destroys, or has the potential to do so, usually over time — an eventuality. Venom is often used to describe harsh speech or hurtful aggressiveness.
Venom is a toxin that is harmful only when it enters the bloodstream, produced by animals of various species.
Poison is a toxin that is harmful when ingested (and, in more general terms, however it gets into the system). It is also a catch-all term for any harmful substance.
Thus there are many venomous snakes, but very few poisonous ones, i.e. ones you would have to eat for them to harm you.
Venom is contained by a living organism, and it is often used as an offensive/defensive measure to ensure survival. Venom is often poisonous to the intended target.
Poison is an item that is harmful or dangerous to the person/thing to which it refers.
Arsenic is poisonous to humans. Cobra venom is also poisonous to humans and other animals. The venom of a "Daddy Long Legs" spider is not considered to be toxic to humans, however.
Venom, poison, and to a lesser extent toxin are informally used interchangeably, referring to all substances that are harmful to living things. Below I will list what is my understanding of their technical differences; but as English is a living and very lax language, and as the words are used in multiple separate scientific fields, I'm sure there is some argument over the matter. Therefore, what I or anyone else tells you about their definitions isn't set in stone, so to speak.
A toxin is any inanimate substance that has an adverse interaction with an individual's biological processes, i.e. not a bacterial or other disease. This is distinct from a substance that damages anything it touches like a corrosive substance, because a toxin only works by exploiting specific biological processes. That is to say, what is toxic to a human being may not be toxic to a bird because their biological processes are different, whereas a corrosive substance is more or less equally damaging to most any creature it touches.
A poison is a toxin that can be absorbed through body tissue. Poisons are thus dangerous to touch or swallow. There are many animals partially or wholly coated in poisons such as dart frogs or even shrews, but snakes are not among them. Poisons also don't need to belong to animals or plants; certain chemical elements such as arsenic, lead, or mercury are poisons usually found outside of any living body.
A venom is a toxin that is not absorbed through the skin or mucous membranes, requiring it to be injected intentionally, such as through snake fangs or insect stingers. This necessarily means that venoms are only found produced within animals and plants. The two kinds of venom are hemotoxins which damage red blood cells and neurotoxins which damage nervous tissue. Presuming there are no cuts or other breaks in the skin or mucous membranes, venoms are completely safe to touch or swallow, but be warned that many people have tiny cuts they aren't aware of, and it's good practice never to touch venom or any toxin without protective equipment anyway.
As venoms are always biologically produced substances, they contain proteins, and so it's possible to have allergies to otherwise mild venoms such as bee stings. Theoretically, you could be allergic to biological poisons such as dart frogs, but it's not possible to have an allergy to a non-biological toxin such as arsenic.
Snakes especially are often referred to as poisonous, but that's usually incorrect - poisonous would mean they were toxic to touch or eat. Many snakes are venomous as they bear and inject venom. There are no snakes who produce their own poison, but the Japanese grass snake and the common garter snake include animals in their diets who are harmless to them but toxic to humans and can pass poisons to humans this way.
Venom is used to refer to the poisonous substances that animals like snakes and scorpions produce.
Poison is used to refer to substances that could harm or even kill somebody through its chemical action.
To illustrate the difference, consider this article: Poison, not snake, killed Cleopatra, scholar says
The article says that Cleopatra may have "died from drinking a mixture of poisons and not from a snake bite." The snake bite would release venom. But Cleopatra drank something to kill herself - that's poison.
This other article explains the same as: Cleopatra Died From Poison. She used hemlock, not snake's venom, says historian
I have copied here a clear distinction between these terms as provided in reference dictionaries.
Poison, toxin, venom are terms for any substance that injures the health or destroys life when absorbed into the system, especially of a higher animal.
Poison is the general word: a poison for insects.
A toxin is a poison produced by an organism; it is especially used in medicine in reference to disease-causing bacterial secretions: A toxin produces diphtheria.
Venom is especially used of the poisons secreted by certain animals, usually injected by bite or sting: the venom of a snake.
You have some good definitions, but I will add a bit of usage.
When someone has been struck down by venom—the bite of a venomous animal, or venom on a blade—they have been poisoned.
When someone has ingested something poisonous they have been poisoned.
Although technically incorrect, people often talk about snakes being poisonous, by which they mean venomous.
Venom is a word that is less commonly used now.
In that respect, in day-to-day usage you can get away with using "poison" when it might be more technically accurate to use "toxin."