I always found it odd that the cure for a venom was an antivenin — and that inflammation of a tendon was tendinitis — but it looks like the sensible term, antivenom, has won out:
The name “antivenin” comes from the French word “venin”, meaning venom, and historically “antivenin” was predominant around the world. In 1981, the World Health Organization decided that the preferred terminology in the English language would be “venom” and “antivenom” rather than “venin/antivenin” or “venen/antivenene”.
Antivenoms are similar to vaccines, but immunity isn’t induced directly in the patient; it is induced in a host animal — a horse or sheep — and the hyperimmunized serum is transfused into the patient:
It is quite possible to immunize a person directly with small and graded doses of venom rather than an animal. According to Greek history, King Mithridates did this in order to protect himself against attempts of poisoning; therefore this procedure is often called mithridatization.
However, unlike a vaccination against disease which must only produce a latent immunity that can be roused in case of infection, to neutralize a sudden and large dose of venom requires maintaining a high level of circulating antibody (a hyperimmunized state), through repeated venom injections (typically every 21 days). The long-term health effects of this process have not been studied.