ar·ca·num (är-kā'nəm) n.
pl.ar·ca·na (-nə) or ar·ca·nums
A deep secret; a mystery.
often arcana 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).
A secret essence or remedy; an elixir.
[Latin arcānum, from neuter of arcānus, secret; see arcane.]