A secret or mysterious knowledge or information, often related to alchemy or esoteric matters. The ancient manuscript was said to contain the arcanum of eternal life.
A preparation or elixir believed, especially in alchemy, to possess remarkable curative or life-prolonging powers. Medieval alchemists searched tirelessly for an arcanum that could banish every illness.
A profound secret or key principle that is essential to understanding a subject or solving a problem. The true arcanum of chess lies in the delicate balance between strategy and tactics.