caustic

Etymology

From the Latin causticus (“burning”), from Ancient Greek καυστικός (kaustikós, “burning”), from καυστός (kaustós, “burnt”) + -ικός (-ikós).

adj

1. Capable of burning, corroding or destroying organic tissue.
2. (of language, etc.) Sharp, bitter, cutting, biting, and sarcastic in a scathing way.
   "How now!" said Scrooge, caustic and cold as ever. 1843, Charles Dickens, A Christmas Carol
   The bargain was not concluded as easily as might have been expected though, for Scadder was caustic and ill-humoured, and cast much unnecessary opposition in the way 1843, Charles Dickens, Martin Chuzzlewit
   Madame Beck esteemed me learned and blue; Miss Fanshawe, caustic, ironic, and cynical 1853, Charlotte Brontë, Villette
   The Secretary and the Assistant-Secretaries would say little caustic things about him to the senior clerks, and seemed somewhat to begrudge him his new honours. 1857, Anthony Trollope, The Three Clerks
   this set of worthies, who were only too prone to shut up their emotions with caustic words. 1886, Thomas Hardy, The Mayor of Casterbridge
   though he came too late / To join the martyrs, there was still a place / Among the tempters for a caustic tongue / / To test the resolution of the young / With tales of the small failings of the great c. 1930, W.H.Auden, The Quest

noun

1. Any substance or means which, applied to animal or other organic tissue, burns, corrodes, or destroys it by chemical action; an escharotic.
2. (optics, computer graphics) The envelope of reflected or refracted rays of light for a given surface or object.
3. (mathematics) The envelope of reflected or refracted rays for a given curve.
4. (informal, chemistry) Caustic soda.