Source : Webster's Revised Unabridged Dictionary (1913)

Brachydiagonal \Brach`y*di*ag"o*nal\, a. [Gr. brachy`s short +
   E. diagonal.]
   Pertaining to the shorter diagonal, as of a rhombic prism.

   {Brachydiagonal axis}, the shorter lateral axis of an
      orthorhombic crystal.