Meanings
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1
noun
a secret, mystery, or piece of knowledge known only to initiates or specialists
The notation was once treated as an arcanum available only to advanced mathematicians.
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2
noun
historical: a supposedly powerful secret remedy or alchemical preparation
The alchemist guarded the recipe for his arcanum from rival practitioners.
Thesaurus
Etymology
Borrowed from Latin arcanum ("secret, mystery"), the neuter of arcanus ("secret, hidden"), from arca ("chest, box"). The plural arcana entered English for hidden doctrines or specialized mysteries.