\Hel"i*coid\, a. [Gr. ?; "e`lix, -ikos, spiral + ?
shape: cf. F. h['e]lico["i]de. See {Helix}.]
1. Spiral; curved, like the spire of a univalve shell.
2. (Zo["o]l.) Shaped like a snail shell; pertaining to the
   {Helicid[ae]}, or Snail family.
{Helicoid parabola} (Math.), the parabolic spiral.

\Hel"i*coid\, n. (Geom.)
A warped surface which may be generated by a straight line
moving in such a manner that every point of the line shall
have a uniform motion in the direction of another fixed
straight line, and at the same time a uniform angular motion
about it.