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This question was closed, but surely "this shape is spiral" is not similar to "this shape is circular/elliptical/helical" in English. (Or rather, in my ears the former comes across as poor English.)

In English, the adjective circular is used for a circle, and the adjective elliptical for an ellipse.

Similarly, the adjective helical is used for a helix, but a helix is 3-dimensional.

What is the corresponding adjective for a spiral?

I offer therefore the chance to provide citations from scholarly papers where spiral is used as adjective. I would happy to learn of a way. I'm not new to English or anything, rather the opposite, but this one has me stumped. Cheers.

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  • 1
    @Greybeard I actually think that "spiral" is in fact different from those other adjectives, as OP says. Voting to reopen the old one.
    – alphabet
    Commented Apr 14, 2023 at 2:07
  • Compare: "This seashell is circular" vs "This seashell is spiral." The latter one sounds invalid to me.
    – alphabet
    Commented Apr 14, 2023 at 2:40
  • @Greybeard I will water your beard and up you one edit to remove that phrase. No-one here has to prove me wrong. I'm less important than the question.
    – Henrik Erlandsson
    Commented Apr 14, 2023 at 2:48
  • 2
    Re-asking question to circumvent closure is not how SE works (and I am surprised to see you got 3 upvotes for the attempt).
    – Joachim
    Commented Apr 14, 2023 at 8:48
  • spiral-shaped?
    – Andreas Rejbrand
    Commented Apr 14, 2023 at 9:54

3 Answers 3

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Spiral is the adjective you’re looking for.

The main thing to understand is that while circular the adjective came from circle the noun, spiral the noun came from spiral the adjective.

Compare:

1) The shape is spiral. → 2) The shape is a spiral.

1) The shape is a circle. → 2) The shape is circular.

From the OED:

spiral, n.
Origin: Formed within English, by conversion. Etymon: SPIRAL adj.1 and adv.
Etymology: Substantive use of SPIRAL adj.1 and adv.

And then:

spiral, adj.1 and adv.
Origin: A borrowing from Latin. Etymon: Latin spīrālis.
Etymology: < medieval Latin spīrālis (Albertus Magnus, a1255), whence also French spiral, Italian spirale, Spanish espiral.

2. Curving continuously round a fixed point in the same plane at a steadily increasing (or diminishing) distance from it.

Amongst these scholarly papers, can you even find spiral as anything but an adjective before dying of boredom?

Source: Oxford English Dictionary (login required)

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  • This doesn't really explain why "this shape is spiral" is invalid.
    – alphabet
    Commented Apr 14, 2023 at 2:38
  • 4
    @alphabet — It’s not invalid.
    – Tinfoil Hat
    Commented Apr 14, 2023 at 2:42
  • It certainly sounds quite wrong to me. I can't find any relevant examples of the phrase "it is spiral" on Google.
    – alphabet
    Commented Apr 14, 2023 at 2:44
  • You have used 1) and 2) in both of your examples, so that I can't address them separately. If your answer retains its structure, I think the first example should be flipped to compare to the 1) and 2) of the second, in order to show that spiral is an adjective. If you can edit the answer so, and you can show that it's used in papers so, I will (as per OP) accept the answer. But it's tricky to show; it may appear so purely to be descriptive and at a loss, as I am, and not as a property of something, as circular is. This property is what I'd like to find for my own writing.
    – Henrik Erlandsson
    Commented Apr 14, 2023 at 3:05
  • @alphabet — Try is spiral or even galaxy is spiral (search in Books for good measure).
    – Tinfoil Hat
    Commented Apr 14, 2023 at 3:18
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Perhaps the confusion arises because noun and adjective have the same forms.

First, some simple examples of various geometric dimensionality where the adjective follows from the noun and has different form:
A circle is circular
A helix is helical
An ellipse is elliptical
A triangle is triangular
A rectangle is rectangular
A line is linear
A plane is planar
A cone is conical
A sphere is spherical

Second, in a smaller number of examples, noun and adjective have the same form:
A square is square
An oval is oval
A spiral is spiral

Here is the abridged M-W entry for spiral:

Merriam Webster
spiral
adjective:
winding around a center or pole and gradually receding from or approaching it
noun:
a the path of a point in a plane moving around a central point while continuously receding from or approaching it b a three-dimensional curve (such as a helix) with one or more turns about an axis

Interestingly, there is a third class which seems to have no adjective from the noun:

A disc is ? {I ignore the contrived “disc-like”}

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  • I think for disc you'd have to use circular or some near-alternative like orbicular, round, peltate, laminar, or lenticular. For example, with leaves, round or orbicular are generally used, even though they could be ambiguous (meaning spherical) in other contexts.
    – Stuart F
    Commented Apr 14, 2023 at 8:30
  • discal
    – Stef
    Commented Apr 14, 2023 at 8:49
  • @Stef Many thanks. A new word for me!
    – Anton
    Commented Apr 14, 2023 at 16:35
  • @Anton I've actually never seen it used anyplace other than that dictionary page. French has the same adjective, and I've only seen it used in the context of medicine, for instance English "spinal disc herniation" translates to French "hernie discale". I think I've read a math paper once where the author used "discular" instead of "discal", probably by analogy with "circular". But the dictionary says "discular" does not exist, so it's possible the author invented it.
    – Stef
    Commented Apr 16, 2023 at 7:31
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To find examples of spiral used as an adjective, you can look at Google Scholar and search for spiral. This produces quite a few uses of spiral as an adjective:

  • spiral structure

  • spiral galaxies

  • spiral imaging

(references)

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  • 5
    To be fair, "spiral" could be seen as a noun adjunct in those examples.
    – alphabet
    Commented Apr 14, 2023 at 1:57
  • Granted that English has its way of sequencing words to make forms/parts of speech dubious, "a spiral structure" etc does not let me express the shape of the structure. The structure is...? The galaxy is...? The last example is better, but the imaging used is magnetic, using magnets, and using a spiral trajectory. So, the trajectory is...?
    – Henrik Erlandsson
    Commented Apr 14, 2023 at 2:56
  • Indeed. We have computer memory, but computer isn't an adjective. So IMHO this A doesn't prove anything.
    – Andreas Rejbrand
    Commented Apr 14, 2023 at 9:59
  • A "spiral spring" is often used in a ball-point pen mechanism. Unfortunately the word is poorly applied - such springs are usually helical.
    – Peter
    Commented Apr 14, 2023 at 10:02

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