noun
: the part of a ray divided in two by double refraction that does not follow the ordinary laws of refraction because its speed varies with its direction in the doubly refracting medium
noun
: the part of a ray divided in two by double refraction that does not follow the ordinary laws of refraction because its speed varies with its direction in the doubly refracting medium
Webster's New International English Dictionary. Новый международный словарь английского языка Webster. 2012