Which term describes a substance that is poisonous to living organisms?

The term that describes a substance that is poisonous to living organisms is toxic. Toxicity refers to the ability of a chemical or substance to cause harm, damage, or adverse effects to living organisms, including plants, animals, and humans. This can include a wide range of effects, from mild irritation to severe health issues or fatalities, depending on the amount, exposure level, and the particular organism involved.

In contrast, "hazardous" is a broader term that encompasses not only toxic substances but also those that might pose risks due to being flammable, reactive, or corrosive. "Corrosive" specifically refers to substances that can cause destruction of living tissue or severe corrosion of materials, while "infectious" relates to pathogens capable of causing disease in living organisms, which is not directly linked to the poison aspect. Thus, the definition provided by the term toxic is the most accurate in this context.