Optic axis of a crystal

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Related to Optic axis of a crystal: double refraction, biaxial crystal
the direction in which a ray of transmitted light suffers no double refraction. All crystals, not of the isometric system, are either uniaxial or biaxial.

See also: Axis

Webster's Revised Unabridged Dictionary, published 1913 by G. & C. Merriam Co.