[" 5.The refractive index of diamond is "2.42." What is the meaning of this "],[" statement? "]

The refractive index of diamond is 2.42. What is the meaning of this statement in relation to the speed of light?

The value of refractive index of diamond is

The value of refractive index of diamond

Refractive index of water is 1.33' - What if the meaning of the statement?