Looking for the History of the Kanji 湯


I was wondering if anyone knows the etymology of this kanji 湯. I'm
specifically looking for the Japanese variation of Bath or "yu". My wife's
last name in kanji is 湯上 (Yugami).




Looking up [the etymology of the Japanese kanji
"湯"](https://en.wiktionary.org/wiki/%E6%B9%AF#Japanese), you will find "From
Old Japanese. Used in the Man'yōshū, completed some time after 759 CE."

And looking up a [Chinese etymology dictionary named
象形字典](https://www.vividict.com/Public/index/page/details/details.html?rid=5095):

>
> 昜，既是声旁也是形旁，是“陽（阳）”的本字，日照，表示天然的温热。湯，金文（水，泉流）（昜，即“阳”，表示天然的温热），表示温泉。篆文承续金文字形。造字本义：名词，天然具有热度的温泉。

Basically translated as:

"昜" is the original word for "陽", meaning natural warmth. You can find the
character "昜" in "太陽", meaning "the sun". And the radical "氵" represents
"water", pronounced 「さんずい」, in kanji such as "泳" or "波". So if you compose "氵"
with "昜", you got "hot spring".

As for the pronunciation, "yu". According to [this
site](https://jisho.org/search/%E6%B9%AF), it's not an on-reading(音読み), but a
kun-reading(訓読み), so it's not related to Chinese pinyin. (By the way, the 音読み
is トウ).

And according to [語源由来辞典](http://gogen-allguide.com/yu/yu.html):

> 湯の語源には、温泉が湧き出る意味の「いづ（出）」の反や、「湧」の字⾳からなど諸説あり、有⼒とされているのは、「ゆるむ（緩む）」の意味とする説である。
> 冷⽔は縮まるようなものであるのに対し、湯は⾝も緩やかになるものなので妥当な説といえる。

The kun-reading(訓読み) is related to 「ゆるむ（緩む）」, which originates from "the
relaxing feeling you get when you get into hot springs".

