Naishou in Buddhism
The Buddhism word, “naishou – 内証 (ないしょう)”, refers to a state in which someone has the complete understanding of Buddhism
in his/her mind. It is very religious and hard to understand. Yet, we can at least understand that that state is a religious secret kept hidden from others.
This is the origin of “naisho – 内緒 (ないしょ)”
and the reason it can mean ‘secrecy’ even though its kanji expression was changed.
And also, this is the reason it focuses more on a state in which something is kept secret rather than a secret itself. }