refractive index refractive • refractively · · · Info · Definitions · Synonyms · Characters · · refractive index · · Text Common · · Latin · · Scripts 16 · · Length 5 · · Syllables Definitions · · · (noun) the ratio of the velocity of light in a vacuum to that in a medium. Synonyms: refractive index, index of refraction. · · Noun Definition 1 Synonyms · · · index of refraction · · Synonym 1 Characters · · space U+0020 a latin small letter a U+0061 c latin small letter c U+0063 d latin small letter d U+0064 e latin small letter e U+0065 f latin small letter f U+0066 i latin small letter i U+0069 n latin small letter n U+006E r latin small letter r U+0072 t latin small letter t U+0074 v latin small letter v U+0076 x latin small letter x U+0078