You might think all knowledge is meant to be shared, but the roots of “arcane” imply a secretive nature. The Latin word “arcānus” means “secret or hidden,” and that comes from “arceō,” which means “to shut something up,” as if in a chest. Over the years, “arcane” has acquired a flavor of the occult about it, but it doesn’t necessarily mean something associated with witchcraft or sorcery. A synonym for the adjective is “esoteric,” which is used to describe things understood by only a select few.