Latin to English definition of Arcanum - Sacred Secret - secret of secrets - noun (pl. arcana) a hidden thing - a mystery or profound secret.
Arcanum - from the Latin, from arcanus - closed, secret - from arca - chest, box - from arcere to shut in.
Arcana - hidden things - 1590s, a direct adoption from Latin of plural of arcanum - adj. arcanus - secret, hidden - (see arcane). Occasionally mistaken for a singular and pluralized as arcanas since arcana is far more common than arcanum.
Arcane 1540s - from arcanus - secret, hidden - from arcere - close up, enclose, contain - from arca - chest, box - from ark - to hold, contain, guard.