caustic surface

American  

noun

Optics.

1. the surface to which all light rays emanating from a single point and reflected by a curved surface, as a concave mirror, are tangent.

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Etymology

Origin of caustic surface

First recorded in 1865–70

Example Sentences

The word she’s looking for is misanthrope, but of course there is a core of tenderness and generosity underneath Elle’s caustic surface.

From New York Times