gyroidal, a. [Gr. gy^ros circle + -oid + -al.].
Spiral in arrangement or action. [1913 Webster]
Having the planes arranged spirally, so that they incline all to the right (or left) of a vertical line; -- said of certain hemihedral forms. [1913 Webster]
Turning the plane of polarization circularly or spirally to the right or left. [1913 Webster]