One of the Japanese words for mind is kokoro. The word koro is the onomatopoeia for “rolling along.” Something that rolls like a ball is koro koro koro. So kokoro is something that is always moving and changing, never stopped. There is no object or form that we can identify as mind. It is always changing. Though we are always looking for something to rely on, we cannot find it in something called mind.
From the excellent book I am reading at the moment:
Shodo Harada , 1940 – Rinzai Zen abbot, Not One Single Thing: A Commentary on the Platform Sutra