Through the years, Usenet evolved into an international forum on thousands of topics, called Usenet news groups, from the arcana of programming languages to European travel tips.
-- Katie Hafner, "James T. Ellis, 45, a Developer of Internet Discussion Network, Is Dead", New York Times, July 1, 2001
Here we must enter briefly into the technical arcana of employment law.
-- Paul F. Campos, JurismaniaThe Madness of American Law
Each arcanum, made visible or tangible by one of these paintings, is the formula of a law of human activity in its relationship with spiritual and material forces whose combination produces the phenomena of life.
-- Lida A. Churchill and Paul Christian, History and Practice of Magic
Arcanum is from the Latin, from arcanus "closed, secret," from arca, "chest, box," from arcere, "to shut in."