caustic

Concise Oxford English Dictionary © 2008 Oxford University Press:
caustic /ˈkɔːstɪk, ˈkɒst-/

▶adjective

• 1 able to burn or corrode organic tissue by chemical action.

• 2 scathingly sarcastic.

• 3 Physics formed by the intersection of reflected or refracted parallel rays from a curved surface.

▶noun

• 1 a caustic substance.

• 2 Physics a caustic surface or curve.

– derivatives
caustically adverb,
causticity noun.

– origin ME: via L. from Gk kaustikos, from kaustos ‘combustible’, from kaiein ‘to burn’.