\U`ni*ax"i*al\, a. [Uni + axial.]
1. (Crystallog.) Having but one optic axis, or line of no
   double refraction.

Note: In uniaxial crystals, the optic axis has the direction
      of the vertical crystallographic axis. All tetragonal
      and hexagonal crystals are uniaxial.

2. (Biol.) Having only one axis; developing along a single
   line or plane; -- opposed to multiaxial.