adjective

1. that can burn, eat away, or destroy tissue by chemical action; corrosive
2. cutting or sarcastic in utterance; biting
3. designating or of the curved radial surface, or a plane curve in this surface, formed by the reflection or refraction of rays from a curved solid surface

Etymology: ME caustik < L causticus < Gr kaustikos < kaustos, burning < kaiein, to burn

noun

1. any caustic substance, esp. caustic soda
2. a caustic surface or curve

Etymology: L causticum < the adj.