The Collaborative International Dictionary of English v.0.48:

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.
      [1913 Webster]

            Inquiries into the arcana of the Godhead.
                                                  --Warburton.
      [1913 Webster]

   2. (Med.) A secret remedy; an elixir. --Dunglison.
      [1913 Webster]

WordNet (r) 3.0 (2006):

arcanum
    n 1: information known only to a special group; "the secret of
         Cajun cooking" [syn: secret, arcanum]

U.S. Gazetteer Places (2000):

Arcanum, OH -- U.S. village in Ohio
   Population (2000):    2076
   Housing Units (2000): 891
   Land area (2000):     1.159879 sq. miles (3.004072 sq. km)
   Water area (2000):    0.000000 sq. miles (0.000000 sq. km)
   Total area (2000):    1.159879 sq. miles (3.004072 sq. km)
   FIPS code:            02330
   Located within:       Ohio (OH), FIPS 39
   Location:             39.991714 N, 84.554797 W
   ZIP Codes (1990):
   Note: some ZIP codes may be omitted esp. for suburbs.
   Headwords:
    Arcanum, OH
    Arcanum