1. mysterious or secret knowledge, language, or information known or understood by very few people
Usage: formal; usually plural

Examples

• The professor delved into the arcana of medieval alchemy.
• Only a few scholars understand the arcana of ancient Greek philosophy.
• The book revealed the arcana of the secret society.
• She was fascinated by the arcana of quantum physics.
• The arcana of the legal profession can be confusing to outsiders.
• He spent years studying the arcana of Renaissance art.