Source : Webster's Revised Unabridged Dictionary (1913)

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.

Source : WordNet®

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