The Collaborative International Dictionary of English v.0.48:

Biaxal \Bi*ax"al\, Biaxial \Bi*ax"i*al\, a. [Pref. bi- + axal,
   axial.] (Opt.)
   Having two axes; as, biaxial polarization; biaxial crystals.
   --Brewster. -- Bi*ax"i*al*ly, adv.
   [1913 Webster]