(a.) Sinuous.

ambagious circuitous circumlocutory cochlear cochleate convoluted convolutional corkscrew corkscrewy flexuose flexuous helical helicoid involute involuted involutional labyrinthine mazy meandering meandrous rivose rivulose roundabout ruffled screw-shaped scrolled serpentine sinuate sinuose sinuous snaky spiral spiroid torsional tortile tortuous turbinal turbinate turning twisting twisty verticillate volute voluted whorled winding wreathlike wreathy