any substance that causes injury or illness or death of a living organism
"The hiker swallowed a poisonous berry and immediately began to vomit from the toxin's effect on his body."
A substance that is harmful or lethal to a living organism when ingested.
"The gardener accidentally watered his plants with a solution containing a toxic chemical intended to kill insects, which proved fatal to the nearby rabbits if they drank from the soil moisture."
In plain English: A poison is something that makes you very sick if you eat it, drink it, or touch it with your skin.
"The old man died after accidentally drinking poison from an open bottle on his porch."
Usage: Use the noun form to refer specifically to toxic substances, while reserving the verb for the act of administering them. Avoid confusing this with "poisonous," which describes something that contains such a substance rather than being an action itself.
To use poison to kill or paralyse (somebody).
"The assassin tried to poison his rival by slipping a deadly substance into the victim's wine glass."
In plain English: To poison something is to put harmful chemicals into it so people get sick if they eat, drink, or touch it.
"The snake bit his leg and injected poison into his bloodstream."
The word "poison" comes from the Latin pōtiōnem, meaning "a poisonous draught" or "drink." It entered English via Old French and originally referred to a liquid intended for drinking that was toxic.