to give someone poison, especially by adding it to their food or drink, in order to harm or kill them:
She was accused in 1974 of poisoning her second husband, Charles.
He killed several people by poisoning their tea.
poison somebody with something
Helms attempted to poison his whole family with strychnine.
if a substance poisons someone, it makes them sick or kills them:
Thousands of children were poisoned by radiation.
to make land, rivers, air etc dirty and dangerous, especially by the use of harmful chemicals:
Pesticides are poisoning our rivers.
to have very harmful and unpleasant effects on someone's mind, emotions, or a situation:
Her childhood had been poisoned by an abusive stepfather.
The law will only serve to poison relations between the US and Mexico.
Television violence is poisoning the minds of young people.
—poisoner noun [countable]