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re·frac·tiv·i·ty .rē-.frak-'tiv-ət-ē, ri- n, pl -ties the ability of a substance to refract light expressed quantitatively specif the index of refraction minus one
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re·frac·tiv·i·ty (re″frak-tivґĭ-te) the quality of being refractive; the power or ability to refract.Medical dictionary. 2011.