Scientists Say: Venomous
When animals have to inject their poisons, they are described using a special word

This rattlesnake can inject poison when it bites, which makes it venomous.
wormwould/Flickr(CC-BY-NC-2.0)
Venomous (adjective, “VEH-nom-us”)
This word describes animals that inject a poison. They may bite or sting. But they have to inject that toxin.
In a sentence
Scientists are using the venom from tarantulas to fight disease.

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Power Words
(for more about Power Words, click here)
poison A substance that causes sickness or death to an organism.
poisonous (In biology) An organism that secretes a toxic substance passively. Plants can be poisonous, as can animals that secrete toxins through their skin.
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.
toxin A poison produced by living organisms, such as germs, bees, spiders, poison ivy and snakes.
venom A poisonous secretion of an animal, such as a snake, spider or scorpion, usually transmitted by a bite or sting.