Dictionary.net

The turning aside of a ray of light when passing the edge of a body that will not admit light; the change suffered by such a ray.

Deviation of rays of light upon entering a small aperture.

A phenomenon consisting in the bending and dispersion of rays of light when passing near the edge of a body. [Lat.]

n. The deflection and decomposition of light in passing by the edges of opaque bodies or through narrow slits, causing the appearance of parallel bands or fringes of prismatic colours.