The Collaborative International Dictionary of English v.0.48:

Pinacone \Pin"a*cone\, n. [From Gr. ?, ?, a tablet. So called
   because it unites with water so as to form tablet-shaped
   crystals.] (Chem.)
   A white crystalline substance related to the glycols, and
   made from acetone; hence, by extension, any one of a series
   of substances of which pinacone proper is the type. [Written
   also pinakone.]
   [1913 Webster]