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.