Definition of: caustic

(kôs′tik) adjective
1. Capable of corroding or eating away tissues; burning; corrosive.
2. Causing to smart; stinging; biting; sarcastic and severe.
3. Optics a Designating a surface to which all rays emitted from one point and reflected or refracted from a curved surface are tangents: so called because along such a surface the heating effect is at the maximum. b Designating a curve formed by such a surface.
—noun
1. A caustic substance.
2. Optics A caustic curve or surface. Also caus′ti·cal. See synonyms under BITTER. [<L causticus <Gk. kaustikos <kausos burning <kaiein burn]
—caus′ti·cal·ly adverb