Source : Webster's Revised Unabridged Dictionary (1913)

Helicoid \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.

Helicoid \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.