Hel"i*coid (?), a. [Gr. &?;; "e`lix, -ikos, spiral + &?; shape: cf. F. hélicoïde. See Helix.]

1. Spiral; curved, like the spire of a univalve shell.

2. (Zoöl.) Shaped like a snail shell; pertaining to the Helicidæ, 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.