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arcanum \ar-KAY-nuhm\ , noun;
plural arcana \-nuh\
1.A secret; a mystery.
2.Specialized or mysterious knowledge, language, or information that is not accessible to the average person (generally used in the plural).
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