Scientists Say: Toxin
This refers to any substance that can kill or harm an organism — and came from a living organism

Don’t touch! This lovely frog’s colors are a sign that it secretes a toxin.
Abi Skipp/Flickr (CC-BY-2.0)
Toxin (adjective, “TOX-in”)
This is something that can harm or kill cells or organisms. It’s a term for a class of things that are poisonous, or toxic. When scientists measure how dangerous a chemical is, they measure its toxicity. The scientists who study these substances are called toxicologists.
But while any substance can be toxic, a toxin is more specific. Toxins are poisonous substances produced by living things. They can be poisons from frog skin or poison ivy, or venom from a snake. But many synthetic chemicals can poison, none of them is a toxin.
In a sentence
While toxic algae can poison some species of plankton, it can make others swim faster.
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Power Words
(for more about Power Words, click here)
toxic Poisonous or able to harm or kill cells, tissues or whole organisms. The measure of risk posed by such a poison is its toxicity.
toxicant An agent, usually some chemical, that can produce poisoning or harmful reactions in a living organism.
toxicology The branch of science that probes poisons and how they disrupt the health of people and other organisms. Scientists who work in this field are called toxicologists.
toxin A poison produced by living organisms, such as germs, bees, spiders, poison ivy and snakes.