秘ひ鍵けん

noun

hidden mysteries; secret principle

Refers to esoteric or profound truths that are not openly revealed, often in religious, philosophical, or mystical contexts. The term is somewhat literary and not an everyday word.

• その経きょう典てんには宇う宙ちゅうの秘ひ鍵けんが説とかれている。

  That scripture expounds the hidden mysteries of the universe.

• 彼かれは長なが年ねんの修しゅ行ぎょうの末すえに、ついにその秘ひ鍵けんを悟さとった。

  After years of training, he finally realized that secret principle.