Caustic is a name given to various substances which burn or corrode the skin or other tissues. As a rule they disintegrate and destroy the structure of all organized substances, for example, cotton-wool, etc.
In optics, cautic is the name given to the curve to which the rays of light, reflected or refracted by another curve, are tangents. Caustics are consequently of two kinds - catacaustics and diacaustics - the former being caustics by reflection and the latter caustics by refraction. Research Caustic