Source : Webster's Revised Unabridged Dictionary (1913)

Pleochroism \Ple*och"ro*ism\, n. [Gr.? mor? + ? color.]
   (Crystallog.)
   The property possessed by some crystals, of showing different
   colors when viewed in the direction of different axes.

Source : WordNet®

pleochroism
     n : the phenomenon of different colors appearing when certain
         crystals are viewed from different directions