The Collaborative International Dictionary of English v.0.48:

Helical \Hel"i*cal\, a. [From Helix.]
   Of or pertaining to, or in the form of, a helix; spiral; as,
   a helical staircase; a helical spring. -- Hel"i*cal*ly,
   adv.
   [1913 Webster]

WordNet (r) 3.0 (2006):

helical
    adj 1: in the shape of a coil [syn: coiling, helical,
           spiral, spiraling, volute, voluted, whorled,
           turbinate]