Resources to better understand the kanji order for kanji using 音読み

Vocabulary in Japanese can appear to be infinite when combining kanji, specifically those using 音読み.

I feel that I have a grasp of how words are formed in 訓読み such as 沈む + 込む for 沈み込む, but I am a bit lost when it comes to words using 音読み. For example, why is the word 核融合反応 follow this particular order and why does 核 comes before 融 in核融合?

I know this is potentially going to get into Chinese, but I was wondering if you knew of resources on this particular topic geared towards people learning Japanese.

If feel that this becomes a requirement to get into more advance texts and articles.

Thank you for your help!

Edit: Here’s ChatGPT answer on that topic:

Question 1:

In Japanese, when using the onyomi, how are words composed of multiple characters structured and how does the position of the character influence the overall meaning?

Answer 1:

In Japanese, when using the onyomi, words composed of multiple characters are structured based on the Chinese characters, known as kanji, that make up the word. Each kanji character has its own pronunciation, meaning, and sometimes even its own onyomi reading. When multiple kanji are combined to form a word, the readings and meanings of each kanji may influence the overall meaning of the word.

For example, let’s take the word “学校” (gakkou), which means “school.” This word is composed of two kanji characters: “学” (gaku), which means “learning,” and “校” (kou), which means “institution.” When these two kanji are combined, the resulting word “学校” means “learning institution” or “school.”

The position of the character can also influence the overall meaning of the word. In some cases, the first character in a word may be used to modify or clarify the meaning of the second character. For example, the word “紅葉” (kouyou) means “autumn leaves,” but the first character “紅” (kou) means “crimson” or “deep red.” So, in this case, the first character “紅” modifies or clarifies the meaning of the second character “葉” (you), which means “leaves.”

In summary, when using the onyomi in Japanese, words composed of multiple characters are structured based on the kanji characters that make up the word, and the readings and meanings of each kanji may influence the overall meaning of the word. The position of the character can also affect the meaning by modifying or clarifying the meaning of the other characters in the word.

Question 2:
Regarding the explanation above, is the second character always used for the main meaning of the word?

Answer 2:
No, the second character in a Japanese word composed of multiple characters is not always used for the main meaning of the word. While it is true that the second character in a compound word is often used to convey the main meaning of the word, this is not always the case.

In some cases, the first character may be used to modify or clarify the meaning of the second character. For example, the word “白鳥” (hakuchou) means “swan,” but the first character “白” (haku) means “white,” which modifies or clarifies the meaning of the second character “鳥” (chou), which means “bird.”

In other cases, the first and second characters may have equal importance in conveying the meaning of the word. For example, the word “新聞” (shinbun) means “newspaper,” but both characters “新” (shin) and “聞” (bun) contribute equally to the meaning of the word.

Therefore, the position of the character in a Japanese word composed of multiple characters does not always determine its importance in conveying the overall meaning of the word.