Don wrote:

....regarding "spiral" vs "helical"...

1 a : the path of a point in a plane moving around a central point while
continuously receding from or approaching it
....

Now please explain how #1a above does NOT describe a spiral stair.
Notice how the word *cone* is not mentioned at all.
....

From 1a (emphasis added)...
...around a central point while continuously receding from or
approaching it

"It" here refers to the central point (axis). The definition isn't all
that well written, but is basically correct. If the stair diameter
increases or decreases as the elevation changes, then it is a spiral--if
it doesn't (as most) it's a helix.