- a substance causing illness or death when eaten, drunk, or absorbed even in relatively small quantities
- anything harmful or destructive to happiness or welfare, such as an idea, emotion, etc.
- in a nuclear reactor, a substance, as boron, that readily absorbs thermal neutrons from a chain reaction, thereby decreasing the reactivity of a reactor core: it is used for safety or control
- Chem. a substance that inhibits or destroys the activity of a catalyst, enzyme, etc. or that interferes with or checks a reaction
OFr < L potio, potion