Heli- Vocab: Of Suns and Spirals

Over five hundred years ago in what is today northern Poland, Mikolaj Kopernik was born. You probably know him as Nicolaus Copernicus, famed for proposing the heliocentric view of the universe. If your history and science is a bit rusty, you can break down heliocentric into its simple Greek-derived components to get the gist of the theory: helios “sun,” kentrikos "pertaining to a center," helio-centric “sun-centered.”

Although both helio- and heli- are considered combining forms that indicate the sun, helio- is much more prominent in sun-centered use. In addition to heliocentric, we find heliograph (telegraphing by flashing reflections of sunlight), heliolatry (sun worship), heliotropism (a tendency to turn toward the sun), and other such forms. In sun-related heli- words, the heli- precedes a vowel, as in heliacal (relating to or near the sun) and helium (an element first detected in the solar spectrum). But heli-without-the-o more commonly indicates something quite different.

Heli- (like the related helico-) can also be derived from the Greek helix “helix; spiral.” Think of the Greek Helicon mountain, the tortuous path to the Muses’ abode. This spiral form gives us non-solar words like helicoid (a flattened spiral), helicopter (an aircraft lifted by blades that spiral around a vertical shaft), and helicopter-related forms such as helipad, heliport, and heli-skiing.

How can you tell whether a heli- word indicates the sun or a helix? Look for that sun-shaped o.  

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