The English word is "secret" The Chinese word is "秘密"
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.
Chinese Language Stack Exchange is a question and answer site for students, teachers, and linguists wanting to discuss the finer points of the Chinese language. It only takes a minute to sign up.Sign up to join this community
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:
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 "secret."