Japanese kanji with different meanings in Chinese

湯 in Japanese refers to "hot water." In Chinese, it means "soup." How common are kanji with different meanings in Chinese? Also, why do differences occur in the first place? Were the meanings in both languages originally the same and gradually diverged over time?

Answer

When the Chinese writing system was introduced to Japan, the Japanese people tried to incorporate the Chinese characters, or Kanji, to the words that means the closest thing in the Japanese language. For example, the word たべる, which is a word that probably existed before monks from China introduced Kanji to the Japanese people. When Kanji is finally introduced, the Japanese people find that the the kanji 食 has the closest meaning to たべる, hence how 食べる is now written with the kanji 食. Inevitably, some meanings did not translate exactly the same when it was introduced to the Japanese language and some differences did arise. Now how exactly did this difference arise, it's open for debate.

Notable differences you will see are examples like 勉強 which means "to study" in Japanese, but it means "reluctance" in Chinese. 大丈夫 which means "Are you alright?" in Japanese and "Grown-up man" in Chinese. 手紙 which means "letter" in Japanese, and in Chinese it means "toilet paper" (I just learned that recently too).　高等学校 which means "high school" in Japanese and "college" in Chinese. As for words with individual Kanji, I can't think of many right now, but I suspect they exist as well, but majority of them I believe are compound Kanji words.

There is another more obvious cases of difference in Japanese kanji and Chinese kanji, and these are known as 和製漢字 (wasei-kanji, not to be confused with 和製英語 wasei-eigo), which means Japanese created kanji. 峠 is one such example. However in this case the Kanji itself does not exist in the Chinese language.

Now, if your goal is to communicate effectively in both languages, it's important to know that majority of the time Kanji in Japanese and Chinese does actually means, or almost means the same thing, what you do need to know is that Kanji will not be used in the same context to say the same thing in Chinese and Japanese. For example, 食 does mean food in both Chinese and Japanese, but you will probably not see Chinese people use the word 食 to mean "to eat" like how the Japanese do. But in the ancient Chinese,食 also means "to eat".For example 食之无味 。And in Cantonese 食 still means "to eat" today.For example 食饭。These are differences in usage, not necessarily differences in meaning.