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Why do we write かぜ (cold) as 風邪, not just 風?

The second kanji (邪) is left unread, so why isn't it redundant?

Perhaps, that's to make sure cold doesn't sound like wind. But then why don't
we read it in the word 風邪 (かぜ)?
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2019-11-19T09:40:24.783
73145
2019-11-19T10:14:40.490
31549
question
kanji
風邪: reading and writing
かぜ in the context of this question has two (related) meanings.

  * The meaning _wind_ is written as 風, because that's how you write _wind_ in Chinese.
  * The meaning _cold (sickness)_ is written as 風邪, because that's how you write _cold (sickness)_ in Chinese (or more specifically, Traditional Chinese medicine).

> The second kanji (邪) is left unread

This is not the correct way to think about it. All non-Chinese readings of
_kanji_ are basically Japanese translations of Chinese words. In principle,
any _kanji_ or a string of multiple _kanji_ can be read with a Japanese
translation that is etymologically distinct from the Chinese word the _kanji_
represents.

  * A Japanese translation-reading for a single character is called _kun'yomi_. Hence, かぜ is a _kun'yomi_ for the character 風.
  * A Japanese translation-reading for multiple characters is called _jukujikun_ (if these readings are _established readings_ ). Hence, かぜ is a _jukujikun_ for the _kanji string_ 風邪. 
    * The character representation of a _jukujikun_ word does not necessarily have a morpheme correspondence between the Chinese characters and Japanese morphemes, so you cannot decompose 風邪 into Japanese morphemes. Hence, 風 in 風邪 is not read as かぜ, and 邪 is not "unread".
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2019-11-19T10:14:40.490
73147
2019-11-19T10:14:40.490
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answer