Toxic substance is a term used to describe any substance that can cause harm to living organisms. POISON and venin are two examples of toxic substances. POISON is a six-letter word that refers to a substance that is capable of causing death or injury if ingested, inhaled, or absorbed through the skin. Venin is a five-letter word that refers to a toxic substance found in the venom of certain animals, such as snakes, spiders, and scorpions. Both POISON and venin can be fatal if not treated quickly.