D defs.my
Entry 2 senses Webster, 1913

Arcanum

/är'-kən-əm/ · Ar·ca·num · IPA /ɑɹˈkeɪnəm/
01 n. A secret; a mystery; -- generally used in the plural.
pl. Arcana
  1. 1.
    A secret; a mystery; -- generally used in the plural.
    “Inquiries into the arcana of the Godhead.” — Warburton.
  2. 2.
    A secret remedy; an elixir.(Med.)