Caustic may refer to: Causticity, the property of a substance that causes corrosion Sodium hydroxide, sometimes called caustic soda Potassium hydroxide, sometimes called caustic potash Calcium oxide, sometimes called caustic lime Caustic (optics), the envelope of light rays reflected or refracted by a curved surface or object, or the projection of that envelope of rays on another surface Caustic (mathematics), the envelope of rays reflected or refracted by a manifold, in differential geome… (More on Caustic)