noun

1. the bending of a ray or wave of light, heat, or sound as it passes obliquely from one medium to another of different density, in which its speed is different, or through layers of different density in the same medium
2. Astron. the bending of the rays of light from a star or planet, greatest when the star or planet is lowest in the sky, so that it seems higher than it really is
3. Optics
   1. the ability of the eye to refract light entering it, so as to form an image on the retina
   2. the measuring of the degree of refraction of an eye

Etymology: LL refractio