What is the hidden meaning of "mi mi", the Chinese word for secret? The English word is &quot;secret&quot;
The Chinese word is &quot;秘密&quot;
I found 禾 means grain, 必 means must.
The second character has 宀 (mián) roof,必 (bì) must and 山 (shān) mountain.
How does it all come together? I believe there is a etymological story here.
You're reading too much into it. The only clue to this meaning in the original characters has now been lost.
You can take a look at the following dictionary excerpt to see exactly what information has vanished:
Outlier:

COMPONENTS
禾
In 秘, 禾 is an empty component. It is a corruption of 礻. The original character was 祕 “god; deity,” from which the meanings “secret, covert, undisclosed” are derived.

密 is a phonetic loan if anything, where it contains the idea of &quot;secret.&quot;