he·lix (hēlĭks) "1. Mathematics A three-dimensional curve that lies on a cylinder or cone ..."

[sear]

n. pl. he·lix·es or hel·i·ces (hĕlĭ-sēz′, hēlĭ-)
1. Mathematics A three-dimensional curve that lies on a cylinder or cone, so that its angle to a plane perpendicular to the axis is constant.



I trust AHD. Not quite sure what they're driving at here.

 

[Shiftless2]

Not sure what your concern is. It's clear that's a correct definition.

From Oxford languages

an object having a three-dimensional shape like that of a wire wound uniformly in a single layer around a cylinder or cone, as in a corkscrew or spiral staircase.

a curve on a conical or cylindrical surface that would become a straight line if the surface were unrolled into a plane.

 

[sear]

Thanks S2 #2.
The cone caught me by surprise. The only portion of the definition I was familiar with was the cylinder, probably in DNA context, or the coil spring that slams the screen door shut.

Bonus:
If an arc is quantified by its radius from a central point (the "focus"?), and that radius in infinite, is the arc a straight line?