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.
© Webster 1913.