Caustic material is a term used to describe substances that are highly corrosive and can cause severe burns. ALKALI and LYE are two examples of caustic materials, both of which have 6 and 3 letters respectively. ALKALI is a type of base that is soluble in water and has a pH greater than 7. LYE is a strong alkaline solution, usually made from sodium hydroxide or potassium hydroxide, that is used for cleaning and in the manufacture of soaps and detergents.