• (a.) Same as Helicoid.
Hel`i·coid'al adjective Same as Helicoid . -- 
helicoidal 1 Forming or arranged in a spiral. 2 Having the form of a flat coil or flattened spiral. 3. Coiled or curving like a spiral. 4. In geometry, a warped surface generated by a straight line moving so as to cut or touch a fixed helix.