We Should Live - Ben Bateman

Venom is a poisonous liquid secreted by snakes and other animals.

Venin is the protein in the venom that is actually toxic, especially with snake venom. Many sources ignore this distinction and call ‘venin’ a synonym for ‘venom’. ‘Venin’ by itself is exceedingly rare, and it’s difficult to research on the internet because it’s also the French word for ‘venom’.

Antivenin is a medicine for snakebite. It’s produced by injecting animals with non-lethal doses of one or more venins, waiting for the animal to produce antibodies against it, and then extracting those antibodies from the animal’s blood.

I would guess (based on this and this) that the medicine’s name refers specifically to ‘venin’ and not ‘venom’ because the people who actually make antivenin need the distinction. When you make antivenin, you don’t just inject raw venom into the animal. You process it and isolate the proteins for which you want antibodies. And the resulting medicine doesn’t just treat bites from a specific snake. The same venin can appear in the venom of various species of snakes, e.g. cottonmouths, copperheads, and rattlesnakes are all closely related. So it makes more sense to write and think in terms of the venins that the medicine will actually treat, rather than the animal’s venom that was distilled into those venins.

‘Antivenom’ is arguably not a word at all; it’s a common corruption of ‘antivenin’. Many writers consider it a synonym of ‘antivenin’, because most people don’t know what venin is and wouldn’t care about the distinction even if they did.

If you want to be a language snob with few friends, then use ‘antivenin’ and make fun of people who use ‘antivenom’. If you want to be understood and are willing to risk being mocked by language snobs, then use ‘antivenom’. As a compromise, you could write something like “antivenin (aka antivenom).”