Kokoro (心 - Heart)

One's mind, that would be basis of human feelings, knowledge, or intention, is called 心 (kokoro) in Japanese.

There is a theory that this word comes from the fact that we called organs of poultry animals 凝る (koru) or 凝こる (kokoru).

Here, the verb "koru" means that something concentrates on one point.

Originally, "kokoro" meant organs, but it came to mean a human's organ (especially heart), and later, it has come to mean a mind.

Also, there is another theory that "kokoro" comes from an onomatopoeia: コロコロ (koro koro), which expresses that something is rotating/changing.

In this theory, it's implied that human mind or thought is easy to change.

Incidentally, if you want to mean a heart of organs, you should say 心臓 (shinzō) by adding 臓 (zō - organ) to 心 (shin - heart).

心

人間の理性・知識・感情・意思などの精神的な働きのもとになるものを、日本語で「心」と言います。

この言葉は、禽獣などの臓腑を見て「凝る」または「凝こる」と言ったのを語源とする説があります。

「凝る」は、一点に集中することなどを意味する動詞です。

もともとは臓腑を表していたのが、人間の内臓（特に心臓）の通称となり、さらには精神の意味に進んだとのことです。

また、何かが転がることを表す擬態語「コロコロ」から転じたという説もあります。

この説では、人の気持ちや思いは変わりやすいことを示唆しています。

ちなみに、臓器の心臓を意味したい場合は、臓物を意味する「臓」を付けて「心臓」と言います。

• Originally, "kokoro" meant organs, but it came to mean a human's organ (especially heart), and later, it has come to mean a mind.
• Originally, "kokoro" meant organs, but it came to mean a human's organ (especially heart), and later, it has come to mean the mind.

  I feel like this sounds more natural.

Your posts (from what I read a long time ago) were always very good and very easy to understand. There are rarely any mistakes too!