A toxin is a poisonous substance.
The word is related to the Latin word toxicum which simply means poison.
In Greed toxikon, means to be poisoned from arrows. To give this word a bit more context, toxon, is the Greek name for a bow. If you have any trouble remembering this, consider the following picture.
The term hormesis might have been more broadly used if it had not been coined by the physician Rudolf Arndt. You see Dr. Arndt was a homeopathic researcher; as a tradition, homeopathy is widely considered to be at the heights of quackery.2
The idea of hormesis is something that can put your mind at ease. Any time you hear a story about small amounts of this-or-that substance in the environment, and about how it might harm you, remember this word. If you can't control the thing that you find yourself worrying about, just think...
In small doses it's probably good for me.
Here is some evidence that small doses of cobalt 60 (which is very toxic!) actually helped over a thousand Koreans who were exposed to it for more than a decade.3
Steve Ludwin eating baby mice and answering questions about longevity https://www.youtube.com/watch?v=8varU-eU30k&list=PLDAB00D2D40C335AC&index=2 ↩