Arcanum

Part of speech: noun

Pronunciation: /ɑɹˈkeɪnəm/

Definitions

1. A piece of knowledge that is hidden from the general public, often linked to mystical disciplines or secretive practices
2. An elusive and specialized truth that is only accessible to a select few who are considered knowledgeable or initiated
3. A secret or specialized knowledge that is generally unknown to the public and often pertains to mystical or esoteric subjects

Etymology: Latin "arcānum" is the neuter of "arcānus," meaning "secret" or "hidden," and it is built from "arca," a chest or box, the same root that gave English "ark" and "archive." So the word's core image is of something shut away in a container. In Latin it could describe a hidden thing of any kind, and its plural "arcana" came to mean the secret matters a community guarded from outsiders. English borrowed the word directly from Latin. It keeps the sense of a hidden thing reserved for insiders, which is why it now usually refers to a body of esoteric knowledge, and it is most often used in the plural, "arcana," for the mysteries of a particular field. The singular form in English still carries that sense of a single guarded truth, now tied to the idea of initiation rather than to a physical box.