Question

define absolute refractive index of a medium.?

Answer 1

a number indicating the speed of light in given medium as either the  ratio of speed of light given in that medium

Answer 2

absolute refractive index is defined as a ratio of the speed of light in the vacuum and in selected medium  

relative refractive index is defined as a ratio of speed of light in two different media

When in relative refrective index ,second medium is vacuum then both will be same

Formula n=c/v