1. a mysterious or secret matter; something known or understood by very few
Usage: formal
2. a supposed great secret of nature that alchemists sought to discover
Usage: historical; alchemy

Examples

• The ancient text contained arcana that scholars had debated for centuries.
• She guarded the arcanum of her success jealously.
• The alchemist spent his life searching for the arcanum that would turn lead into gold.
• The professor hinted at arcana within the field that only experts could comprehend.
• Medieval texts often referred to medical arcana known only to physicians.
• The organization’s arcanum was passed down through generations of members.