arcana (n.)youdaoicibaDictYouDict[arcana 词源字典]
"hidden things, mysteries," 1590s, a direct adoption of the Latin plural of arcanum "a secret, a mystery," from neuter of adjective arcanus "secret, hidden, private, concealed" (see arcane). Occasionally mistaken for a singular and pluralized as arcanas because arcana is far more common than arcanum.[arcana etymology, arcana origin, 英语词源]