helicoid

from The American Heritage® Dictionary of the English Language, 5th Edition.

• adjective Arranged in or having the approximate shape of a flattened coil or spiral.
• noun A surface in the form of a coil or screw.

from The Century Dictionary.

• noun A helicoid parabola.
• Pertaining to or having the form of a helix; screw-shaped; coiled like a helix. See cut under Foraminifera. Also helicoidal.
• In conchology, pertaining to or resembling the Helicidæ
• noun In geometry, any one of several different surfaces. See the phrases below

from the GNU version of the Collaborative International Dictionary of English.

• adjective Spiral; curved, like the spire of a univalve shell.
• adjective (Zoöl.) Shaped like a snail shell; pertaining to the Helicidæ, or Snail family.
• adjective (Math.) the parabolic spiral.
• noun (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.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• adjective Having the form of a flattened helix
• noun mathematics A minimal surface in the form of a flattened helix.