\Gy*roid"al\, a. [Gr. ? circle + -oid + -al.]
1. Spiral in arrangement or action.
2. (Crystallog.) Having the planes arranged spirally, so that
   they incline all to the right (or left) of a vertical
   line; -- said of certain hemihedral forms.
3. (Opt.) Turning the plane of polarization circularly or
   spirally to the right or left.