Could 十角形、九角形、七角形 be read as デカゴン、ノナゴン、ヘパタゴン？


As per [dic.yahoo.co.jp](http://dic.yahoo.co.jp/) the following four geometric
figures seem to be read as (ateji / gairaigo)
[十角形](http://dic.search.yahoo.co.jp/search?ei=UTF-8&p=%E5%8D%81%E8%A7%92%E5%BD%A2&stype=full&fr=dic)、[九角形](http://dic.search.yahoo.co.jp//search;_ylt=A2Riol2N7odY2EQA7g9Umfd7?p=%E4%B9%9D%E8%A7%92%E5%BD%A2&stype=full&aq=-1&oq=&ei=UTF-8)、[七角形](http://dic.search.yahoo.co.jp//search;_ylt=A2RCK_EF74dY63kAPQlUmfd7?p=%E4%B8%83%E8%A7%92%E5%BD%A2&stype=full&aq=-1&oq=&ei=UTF-8)、[十二角形](http://dic.search.yahoo.co.jp//search;_ylt=A2RimV87.odYnRcANiBUmfd7?p=%E5%8D%81%E4%BA%8C%E8%A7%92%E5%BD%A2&stype=full&aq=-1&oq=&ei=UTF-8)
( _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?

**七角形{ヘプタゴン}**

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

**九角形{ノナゴン}**

**十角形{デカゴン}**

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

**十二角形{ドデカゴン}**

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？




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.




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.

