|a gadget; dingus; thingumbob.|
|an extraordinary or unusual thing, person, or event; an exceptional example or instance.|
|index of refraction|
|another name for refractive index|
|index of refraction
A measure of the extent to which a substance slows down light waves passing through it. The index of refraction of a substance is equal to the ratio of the velocity of light in a vacuum to its speed in that substance. Its value determines the extent to which light is refracted when entering or leaving the substance.