caustic
caus.tic \'ko.-stik\ \-sti-k*l\ \-sti-k(*-)le-\ \ko.-'stis-*t-e-\ aj [L causticus, fr. Gk kaustikos, fr. kaiein to burn; akin to L]ith kule` smut of plants 1: capable of destroying or eating away by chemical action : CORROSIV E 2: SHARP, INCISIVE {~ wit} 3: relating to or being the envelope of rays emanating from a point and re flected or refracted by a curved surface - caustic n