Lewis & Short

2. Arcānus, a, um, adj. [Arcae], of or pertaining to Arcœ hence, subst.

  1. A. Arcāni, ōrum, m., the inhabitants of Arcœ, Inscr. Orell. 4007.
  2. B. Arcānum, i, n., a villa of Q. Cicero, in the neighborhood of Arcœ, Cic. Att. 5, 1; id. ad Q. Fr. 3, 1 al.