Gy-roid'al, a.

a. [Gr. γῦρος, circle, and εἶδος, form.] 1. Spiral in arrangement or action. 2. (Crystallog.) Having certain planes arranged spirally, so that they incline all to the right, or all to the left, of a vertical line. 3. (Opt.) Turning the plane of polarization circularly or spirally to the right or left.