What is the proper way to write "cube" in romaji?


I have been trying to search for the Romaji version of "cube" without too much
success. There seem to be several variations on the word, although that is
true with almost any version of a Japanese word in any form. I have so far
seen _sanjou_ , _rippou_ , and even _kyuubu_. Am I entirely off track?




三乗【さんじょう】 ( _sanjou_ ) and 立方【りっぽう】 ( _rippou_ ) mean "cube" as in "raise to
the third power". If you want to talk about cubing numbers, you should say
something like 「４の三乗は６４」, which means "the cube of 4 is 64". 立方 is used in
constructions like 「立方メートル」 "cubic meter" and 「立方数」 ["perfect cube
[number]"](https://oeis.org/A000578).

キューブ ( _kyuubu_ ) means "cube" as in "a polyhedron with six square faces",
e.g. 「アイスキューブ」 "ice cube". I don't think you would use キューブ by itself to refer
to the polyhedron; it only seems to be used in loaned compound constructions
like 「ルービックキューブ」. [Google Image searching for just
`キューブ`](https://www.google.com/search?safe=active&tbm=isch&q=%E3%82%AD%E3%83%A5%E3%83%BC%E3%83%96&oq=%E3%82%AD%E3%83%A5%E3%83%BC%E3%83%96)
appears to mostly return pictures of the [Nissan
Cube](http://en.wikipedia.org/wiki/Nissan_Cube), for what that's worth.

Other related words: 立方体【りっぽうたい】 ( _rippoutai_ ) also means "cube" as in "a
polyhedron with six square faces". In mathematical parlance, you would use 立方体
rather than キューブ. If you want a very technical way of referring to a cube in
the polyhedron sense, you can also say 正六面体【せいろくめんたい】 ( _seirokumentai_ ),
which appears to be a calque of "regular hexahedron". Of course, people don't
really say "regular hexahedron" in English, and it seems like 正六面体 is
similarly uncommon in Japanese.

So, to answer your title question - which word is "proper" depends on context.




三乗【さんじょう】 ( _sanjou_ ) and 立方【りっぽう】 ( _rippou_ ) mean "cube" as in "raise to
the third power". If you want to talk about cubing numbers, you should say
something like 「４の三乗は６４」, which means "the cube of 4 is 64". 立方 is used in
constructions like 「立方メートル」 "cubic meter" and 「立方数」 ["perfect cube
[number]"](https://oeis.org/A000578).

キューブ ( _kyuubu_ ) means "cube" as in "a polyhedron with six square faces",
e.g. 「アイスキューブ」 "ice cube". I don't think you would use キューブ by itself to refer
to the polyhedron; it only seems to be used in loaned compound constructions
like 「ルービックキューブ」. [Google Image searching for just
`キューブ`](https://www.google.com/search?safe=active&tbm=isch&q=%E3%82%AD%E3%83%A5%E3%83%BC%E3%83%96&oq=%E3%82%AD%E3%83%A5%E3%83%BC%E3%83%96)
appears to mostly return pictures of the [Nissan
Cube](http://en.wikipedia.org/wiki/Nissan_Cube), for what that's worth.

Other related words: 立方体【りっぽうたい】 ( _rippoutai_ ) also means "cube" as in "a
polyhedron with six square faces". In mathematical parlance, you would use 立方体
rather than キューブ. If you want a very technical way of referring to a cube in
the polyhedron sense, you can also say 正六面体【せいろくめんたい】 ( _seirokumentai_ ),
which appears to be a calque of "regular hexahedron". Of course, people don't
really say "regular hexahedron" in English, and it seems like 正六面体 is
similarly uncommon in Japanese.

So, to answer your title question - which word is "proper" depends on context.

