ALL meanings of relative index of refraction
rel·a·tive in·dex of re·frac·tion
R r - noun relative index of refraction 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. 1