What is the etymology of レントゲン (X-Ray) < From Genki II Lesson 12>?

Is it a borrowed word <外来語> from another language?

Translate suggests using X線 instead of レントゲン, but I'm not sure what the differences are. (Is レントゲン older?)

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    etymology ? ドイツ人の「レントゲン」さんじゃないの・・・ この人→ ja.wikipedia.org/wiki/…
    – chocolate
    Commented Apr 7, 2020 at 17:21

4 Answers 4


レントゲン is named after the inventor of the X-ray, Wilhelm Röntgen (ウィルヘルム・レントゲン) — who named them X-rays, whence the confusion.

A number of words in Japanese medical terminology were adopted from German (a popular example being カルテ from German Karte). I guess it would not be surprising if レントゲン was also imported already as a medical term for X-ray, from German Röntgenbild ("Röntgen image").

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    See also the Wikipedia article on X-rays, which notes that many other languages use a variation of the term "Röntgen radiation" as the name for this phenomenon. Commented Apr 7, 2020 at 19:53
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    ウイルス is another one from German, as is エネルギー (not medical).
    – user36788
    Commented Apr 7, 2020 at 23:07
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    Thanks for the wonderful answer! Is there any difference or modern usage between レントゲン and X線? Commented Apr 7, 2020 at 23:14
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    @SarahSzabo As the name of a medical examination, レントゲン is more common and casual, whereas X線 is more like jargon. X-ray as a physical phenomenon is always X線.
    – naruto
    Commented Apr 8, 2020 at 0:52

I guess, this word based on name of Wilhelm Conrad Röntgen, german physicist, who first detect electromagnetic radiation in this (X-ray) range. It's similliar with russian colloquial word for X-ray detector ー "Рентген" (pronounce like "ˈrentjən").


Its just the German word for it. German does not use X-Ray, it's Röntgenstrahlung or just Röntgen for short. You can even use it as a verb.


Japanese people sometimes localize loan words keeping only the proper noun and omitting the common noun.
Röntgenstrahlung → レントゲン線 → レントゲン
Baumkuchen → バウムクーヘン → バウム

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    The Baum in Baumkuchen is not a proper noun -- it's the common noun meaning "tree". See the Wiktionary entry here. All nouns in German are capitalized, not just proper nouns. In fact, all nouns used to be capitalized in certain varieties of written English as well -- which is why things like the US Constitution or Bill of Rights look a little strange today. Commented Apr 9, 2020 at 4:40
  • Excuse my English, with "the proper noun" I mean the more specific noun preceding in the phrasal noun. Another noun to consider is: B&W film → 白黒フィルム → 白黒
    – Bean
    Commented Apr 11, 2020 at 5:39

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