Kunyomi and Onyomi made Simple

Japanese kanji has two types of readings.

• Onyomi: which is based on the original Chinese pronunciation.
• Kunyomi: which is the reading for native Japanese words. These are words that were in the Japanese language way back before Japan even had a writing system.

Basically…

Each Kanji has multiple readings.
And we separate those readings into 2 categories.

We call the 2 different categories of Kanji readings Onyomi and Kunyomi.

The first category, Onyomi are close to the Chinese reading.

The second category, Kunyomi was made by the Japanese.

A Little Deeper

The Onyomi pronunciation does not have any meaning by itself. The individual Kanji characters have meaning but if you were to just talk using the Onyomi reading it would be like talking with letters of the alphabet. No one would know what you were saying. Usually, the Onyomi reading is used for Japanese words with two Kanji characters.
https://japaneseuniverse.com/2024/02/18/pac-man-in-japaneseconcepts-behind-development-to-global-icon/
Kunyomi on the other hand does have meaning. The Kunyomi pronunciation of Kanji are also full Japanese words. You could start saying the Kunyomi pronunciation of characters and people would understand you. The reason is that you would be saying actual Japanese words instead of just sounds.

Why are there 2 categories?

Well, Kanji originally came from China.
When Kanji was first brought over to Japan, the Chinese told the Japanese that the symbol 雨 meant rain and was pronounced in Chinese as u.

And the Japanese said,

“Oh, I see. We call rain, ame in Japanese”.

So in the end, the Japanese read 雨 all of the above, u and ame.

That is why Kanji has multiple readings. And the original sound from China is called Onyomi and the sounds from Japanese are called Kunyomi.

So, looking at the Kanji 雨,

u would be Onyomi
ame would be Kunyomi.

Onyomi

Onyomi is what we call the Chinese-based sounds.
Although they are not exactly the same as in Chinese.

Kunyomi

Kunyomi is what we call the Japanese sounds.
These are the sounds of the Japanese words that were spoken in Japan before Kanji was adopted.

How do you know when to use which?

When one word has multiple Kanjis, it is read with Onyomi.
When one word has only one Kanji, it is read with Kunyomi.

For example, take the Kanji below

音 (oto)

This Kanji means “sound” and it is read as oto in Kunyomi.
When you see this Kanji in the word

音楽 (ongaku)

音 is read in Onyomi as on.
If you are curious, this word means music.

There are exceptions though. But this is a good rule of thumb to follow.

If you want to learn more Japanese I reviewed a dictionary of grammar series which I personally recommend and use myself.

I also have several other posts on various topics on Japanese Universe if you are interested.