Dictionary
in'dex of refrac'tion
Optics.
a number indicating the speed of light in a given medium as either the ratio of the speed of light in a vacuum to that in the given medium
(absolute index of refraction) or the ratio of the speed of light in a specified medium to that in the given medium
(relative index of refraction). Symbol: n Also called
index, refractive index. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.