Source : Webster's Revised Unabridged Dictionary (1913)

Arcanum \Ar*ca"num\, n.; pl. {Arcana}. [L., fr. arcanus closed,
   secret, fr. arca chest, box, fr. arcere to inclose. See
   {Ark}.]
   1. A secret; a mystery; -- generally used in the plural.

            Inquiries into the arcana of the Godhead.
                                                  --Warburton.

   2. (Med.) A secret remedy; an elixir. --Dunglison.

Source : WordNet®

arcanum
     n : information known only to a special group; "the secret of
         Cajun cooking" [syn: {secret}]
     [also: {arcana} (pl)]