An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

1) Beyond what is usual, ordinary, regular, or established.
2) Exceptional in character, amount, extent, degree, etc. (Dictionary.com). → unordinary.

→ extra-; → ordinary.

When a beam of → unpolarized light is incident on a → doubly refracting crystal, there will be two refracted rays. The ray for which → Snell's law does not hold.

→ extraordinary; → ray.