Caustic meaning : Any substance or means which, applied to animal or other organic tissue, burns, corrodes, or destroys it by chemical action; an escharotic. The envelope of reflected or refracted rays of light for a given surface or object. The envelope of reflected or refracted rays for a given curve. Caustic soda. Capable of burning, corroding or destroying organic tissue. (of language, etc.) Sharp, bitter, cutting, biting, and sarcastic in a scathing way.