As per dic.yahoo.co.jp the following four geometric figures seem to be read as (ateji / gairaigo) 十角形九角形七角形十二角形 (decagon, nonagon, heptagon, dodecagon). As per the same dictionary, all the other sided figures that have less than 12 sides, ((triangle ---> 6-sides) + octagon + 11-sides), are read using each kanji's standard 音読み。

So, are these readings ok?


八角形{はっかくけい} <--- for some reason, normal 音読み reading.



十一角形{じゅういちかくけい} <--- for some reason, normal 音読み reading.


Are those less commonly known English names (the only one an English native speaker might know is "decagon") for geometric shapes burrowing their way into the Japanese language as "ateji / gairaigo"? Or, is it that I'm not understanding the *dic.yahoo.co.jp" dictionary, and "〜角形" is a straight-up normal counter that is read with standard 音読み?

  • 1
    Heptagon should be ヘタゴン. Jan 25, 2017 at 2:22

2 Answers 2


No, those -ゴン words are basically rare loanwords and they're not used in ordinary math classes. (Of course ペンタゴン is famous as the name of a building.) The dictionary entries you linked just say that the katakana word ヘキサゴン means 六角形, etc. They do not say that 六角形 is read as ヘキサゴン, etc. 七角形 does not seem to be in the same dictionary, but it's simply because the rule is fairly simple and the meaning of 七角形 is too obvious to Japanese readers.

  • 三角形: さんかくけい
  • 四角形: しかくけい
  • 五角形: ごかくけい
  • 六角形: ろっかくけい
  • 七角形: しちかくけい / ななかくけい
  • 十二角形: じゅうにかくけい

... and so forth.

かくけい can be replaced with かっけい.

  • I was hoping that was then answer! I can't even remember in English what nonagons, dodecagons, etc. are. Jan 25, 2017 at 1:51

Not to confuse the issue (hopefully), but it bears noting that any Japanese word could be given just about any reading -- that's what furigana are for.

Interesting examples I've run across include:

  • 騎士, usually read as きし{kishi}, with the furigana ナイト{naito} instead to match the English word "knight".
    (Though I suppose, to match Monty Python, perhaps クニギット{kunigitto} would be more fitting. :) )
  • 本気, usually read as [ほんき]{honki}, with the furigana マジ{maji} instead to convey an alternate meaning.
  • 玄人, usually read as くろうと{kurōto}, with the furigana プロ{puro} instead to match the English word "pro".

Manga are chock full of numerous examples of furigana used to apply different readings to words. Furigana are a wonderful feature of Japanese writing, providing authors with a means to give any word additional layers of meaning.

That said, in a more specific reply to your question "are these readings ok," there are standard readings of Japanese words, and readings that only come from furigana. Furigana for any given term might be providing the standard reading. However, if you see a kanji term with katakana furigana, chances are high that the furigana reading in these cases is non-standard, and only specific to the text containing this reading.

  • I always found it easier to explain to new learners of the Japanese language that furigana is a reading guide and should always be treated as such - a guide. It also works the other way around when kanji are supposed to explain to native readers "what does this weird foreign word mean?" And sometimes, not often, some publishers will pull kanji up, though I have yet to find out why because it's hell of a lot difficult to figure small, blurred signs out. I've also seen an instance of kanji in the bottom part and kanji in the upper part, though it must have been some buddhist or arcanic term.
    – szychy
    Feb 15, 2017 at 2:18

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