arcanum

The archaeologist believed the symbol was an arcanum that could reveal the tomb's location.

用法提示：这里 arcanum 作名词，意为“秘密、奥秘”，用单数形式指一个特定的秘密。

Few outsiders have ever learned the arcana of the island's boat-building tradition.

用法提示：arcana 是 arcanum 的复数形式，表示“奥秘、秘传知识”。

The old cook guarded the arcanum of her family's noodle soup as if it were gold.

用法提示：arcanum 在此作名词，特指“秘方”，并接 of 说明所属对象。