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As a non-native English speaker I struggle with Greek prefixes. Am I allowed to use just normal English numbers in place of them? Is it natural? Or do I have to learn how those Greek prefixes work at the end of the day?

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    You would call it an eight-sided polygon. Not eight-gon. And you could do that in a great many languages not just English. But maybe more to the point, you could also just say octagon in all these languages. So if you just learn that, you actually save yourself work in the end because everyone will understand you from New York to Paris to Berlin to Moscow. And also, those prefixes are incredibly useful for other things and pop up in all kinds of other places. Octopus, octave, October. Decade, decimal, December. You will end up learning all of them anyway. You already have. – RegDwigнt Dec 11 '18 at 21:50
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    In the US, at least, you can say pretty much anything you want -- you (probably) won't be shot for it. The terms you suggest would be generally understood, and I think they are quite acceptable coming from someone who clearly has an incomplete command of the language. If, however, you will be talking in an academic environment you probably should take the effort to learn the correct terms. (Personally, I kind of detest the ordinals -- I think they should be "wonth", "tooth", "threeth", "forth", and "fifeth".) – Hot Licks Dec 11 '18 at 22:02
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    @RegDwigнt "Octopus, octave, October. Decade, decimal, December." It perhaps confuses the issue given that October and December are the 10th and 12th months, respectively. – josh314 Dec 12 '18 at 5:11
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    @josh314 it doesn't confuse the issue, quite the opposite. It makes you wonder, okay, so why the heck is the 12th month called the tenth? And the 9th month called the seventh? And that makes you research it, and you find out something new and exciting. And you've learned something else completely for free, just because you refused to say ten-gon. Isn't that wonderful. – RegDwigнt Dec 12 '18 at 9:56
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    Why even call them '-gons' if you want to avoid greek? – TaW Dec 12 '18 at 13:05
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Mathematicians do use this form for bigger numbers. The Wikipedia article Heptadecagon currently contains the phrase "a regular 51-gon, 85-gon or 255-gon and any regular n-gon with 2h times as many sides".

And in that context, you may find mathematicians using the form for smaller numbers: in an article about polygons of different sizes, I would not be surprised to meet "5-gon" or "8-gon".

But outside mathematics, I've never heard anybody say "eight-gon" or any of the others.

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    I would distinguish between "8-gon" and "eight-gon" here. When using a number, it can be considered as a substitution of the "n". "Eight-gon", however, would imply that this is a defined English word. This is similar to "with 2h times" where both 2 and h are used in a mathematical, not linguistic, sense. – Flater Dec 12 '18 at 8:53
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    Colin, have you heard "eight-gon" spoken in a mathematics sense? My understanding is (similar to @Flater's) that "8-gon" would be proncounced "octagon" and the use of "number-gon" in speech would kick in when the speaker doesn't know or can't be bothered to work out the prefix. But I'm not an expert – Chris H Dec 12 '18 at 9:57
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    No. @ChrisH, I don't think I've ever discussed such things in person! I'm not sure what I would say. – Colin Fine Dec 12 '18 at 11:00
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    Anybody using a greek prefix for a 27-gon is a clasically educated show-off! In written English outside the realm of mathematics I'd write 27-sided polygon (27-gon) and then use the abbreviation introduced in the brackets and the obvious generalization thereof. In speech I'd similarly make the usage clear the first time I used it. – nigel222 Dec 12 '18 at 11:15
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    @ChrisH As a mathematician I can attest that 8-gon is not pronounced "octagon." It's pronounced "eight-gon." – Matt Samuel Dec 13 '18 at 2:22
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Short answer: no.

Longer answer: you will probably be understood, but people will think it's strange. Almost all words in English have roots in other languages. For these words, you have correctly identified Greek as the original language. Curiously, you have taken exception with the prefixes, but not the suffix: -gon, which is also Greek.

As a more interesting case, triangle uses the -angle suffix, which comes from Latin.
( tri- is both a Greek and Latin prefix.)


Personal note:
In my travels as a mathematician, I admit that I have heard and used n-gon a lot. When a mathematical discussion involved specific instances of an n-gon, it was sometimes most natural to say things like eight-gon; especially when other, higher -gon were included in the discussion. Outside of the context of pure maths, it would be extremely unusual for anyone, even a mathematician, to say eight-gon.

  • I wouldn't say "almost all" ... en.wikipedia.org/wiki/… – Azor Ahai Dec 12 '18 at 1:01
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    And while less common than quadrilateral (literally meaning "four-sided"), quadrangle is perfectly valid for a 4-gon. – Ben Voigt Dec 12 '18 at 3:59
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    @BenVoigt The bygone tetragon. – jxh Dec 12 '18 at 6:06
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    @AzorAhai "Almost all" is right by count in a dictionary, but not by usage. Search for "Uncleftish beholding" to see what English would look like without foreign words. – Martin Bonner Dec 12 '18 at 6:48
  • +1. Note that you could explain the word when you use it for the first time, e.g. "an enneagon (nine-sided polygon)". – Rosie F Dec 13 '18 at 8:22
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Am I allowed to use just normal English numbers in place of them?

No. There is no such word as eightgon.

Is it natural?

No. If I heard "eightgon" I would think I heard "eight gone" or "ate gone". You can't just make up words like that.


You may as well replace "triangle" with "threegon", or "rectangle" with "fourgon". No-one will understand you, and the purpose of language is to be understood.

  • Yes, thank you for this answer. I would also be confused and not immediately make the connection that the OP wants me to make. Also, "fourgon" is homophonous with an existing word, "forgone", so that would definitely be confusing – Ben Sandeen Dec 12 '18 at 16:16
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    @NickGammon You may as well replace "triangle" with "threegon", or "rectangle" with "fourgon". No-one will understand you, and the purpose of language is to be understood. And everyone will understand me if I say Tetracontagon? I don't think so. – Happy Dec 12 '18 at 17:35
  • For kicks, here are an illustrated two-gon - and one-gon . – Beanluc Dec 12 '18 at 18:33
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    I did, I just didn't mention it, but here it is again – Beanluc Dec 12 '18 at 19:59
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    @Happy And everyone will understand me if I say Tetracontagon? Indeed not, however Tetracontagon was not mentioned in the question. – Nick Gammon Dec 13 '18 at 1:06
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"Octagon" and "hexagon" are well established and "common" English words because of the corresponding shapes occur frequently in nature (honeycombs, crystals, etc) and in architecture.

"Pentagon" is commonly used as shorthand for the US Department of Defense (from the shape of its headquarters building).

"Heptagon" is not so common, but it is used to describe the shape of the UK 50 pence and 20 pence coins - though amusingly, one coin dealer has invented the adjective "heptagonical" instead of the standard "heptagonal"! (ref: https://www.westminstercollection.com/p-201P/UK-50-New-PenceCirculation-50p.aspx).

For more than 8 sides, the usual British English terminology is simply "[number]-sided," though decagon and even more rarely dodecagon (the shape of the new UK £1 coin) are used.

Even "three-sided" and "four-sided" are often used in non-mathematical contexts, especially when the object being described is not a regular shape like a square or rectangle. Using "eight-sided" instead of "octagonal" would not sound strange in most non-technical contexts.

Note that for "four-", both Latin and Greek prefixes are used in English - quadrilateral, quadriceps, etc (Latin), and tetrahedron, tetraplegic, etc (Greek). The same applies to "bi-" (Latin) and "di-" (Greek) for "two-".

  • Nice answer. Interestingly, heptagon and decagon are used about equally in modern times (post-1950) while dodecagon and nonagon are only about a third as common - but nonagon is still twice as popular as nine-sided! – Chappo Dec 12 '18 at 22:01
  • @Chappo I suspect nonagons are rare enough that you'd mostly find them in mathematical contexts, where people are more likely to know the proper prefix. – John Montgomery Dec 12 '18 at 22:50
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Older Germanic languages had very few nouns and adjectives to describe geometric shapes. English had native words for a circle, trendel and hring, an arch boga, cf. Ger. Bogen, and words for three- and four-cornered, _ þriscíte_ and, variously spelled, feoðerscéte , feðerscíte , fiðerscýte , fyðerscýte.

Square, from Old French esquire, first entered English as a carpenter’s square mid 13th c., a square shape/area in the late 14th c., and finally as a rectangle with equal sides in the 1550s. This would suggest that a carpenter couldn’t use a square to draw the eponymous shape for well over a century.

Triangle was borrowed directly from French in the late 13th c.

The most common names for polygons, with 5–8 sides, entered English from Greek via Latin in the 1560s. This tells you a great deal about the systematic study of geometry in England as pentagonon and octagonon lost their endings to become what we call them today. You’re basically stuck with them. Such bizarre grecogermanic hybrids like *five-gon do not exist.

Other Germanic languages went through a similar process, but the names of polygons were calqued into native words: Ger. Dreieck, lit. ‘three-corner’, just as Old English, but as nouns, Viereck, Achteck, etc. Cf. Dutch driehoek, Danish and Norwegian trekant (same meaning, different root), but Swedish triangel.

The Greek and Latin cardinal and ordinal numbers pop up in so many English and international words that it pays to learn them, sextuplets, quad bike, bicycle, tricycle, mononucleosis, and on and on.

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    I should add that to my ear ‘85-angle’ (by analogy with ‘triangle’ sounds better and makes easier sense. – Tuffy Dec 12 '18 at 0:41
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    @Tuffy Strange, "85-angle" makes me think of a 85° angle first and foremost, especially if I were to see it in writing. – undercat Dec 12 '18 at 8:22
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As a non-native English speaker I struggle with Greek prefixes.

Nothing that can't be remedied with few hours of study.

Am I allowed to use just normal English numbers in place of them?

Who is your audience, if you are talking to another math person then
are you using them for uniformity/clarity or just to cover your own lack of understanding of few prefixes?

Does pi-gon or zero-gon or (-3)-gon make sense to you? how about 0,1,2, n , 2*n gons?

You can invoke decree of creative license and get away with it, as long as you are adding to the total sum of knowledge and not doing it to cover lack of your own understanding.

Is it natural? Or do I have to learn how those Greek prefixes work at the end of the day?

Do you think a professional in their chosen profession is suppose to know the common vocabulary of their field?

This question has nothing to do with usage of English language but all to do with going the extra mile of being a professional, so to sum it up

For sake clarity/uniformity/communication and depending on the target audience yes. But just to not learn something then no.

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yes you can as long as you are consistent, "gon" is greek and should be replaced too with "side shape". So hexagon gets replaced with "six side shape". You'll soon find learning the greek prefixes more convenient.

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