A caustic compound is a substance that is highly corrosive and can cause severe burns. The term is used to describe four substances: phenol (6 letters), ACID (4 letters), LYE (3 letters), and POTASH (6 letters). Phenol is an aromatic organic compound that is used in the production of plastics, drugs, and dyes. ACID is a corrosive substance that can dissolve metals and other materials. LYE is a strong alkaline solution, usually made from sodium hydroxide or potassium hydroxide. POTASH is a potassium-rich mineral that is used in fertilizers and other industrial products.