- A deep secret; a mystery. (noun)
- Specialized knowledge or detail that is mysterious to the average person: "knows the arcana of police procedure and the intricacies of litigation” ( George F. Will). (noun)
- A secret essence or remedy; an elixir. (noun)
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.