arcanam

[Lat. arcanum, neut. sing. of adj. arcanus, neut. pl. arcana. In Ger. & Fr. arcanum; Sp., Port., & Ital. arcano.] I. Gen.: Anything hidden, a secret. Anything difficult to explore. (Generally in the plural , arcana = secrets.) which, until traced by Newton up to this their origin, had ranked among the most inscrutable arcana of astronomy,..."- Herschel : Astron . (5th ed.), § 230 II. Specially : 1. Med.: An undivulged remedy, or what pa es for such. 2. Alchemy & Old Chem. A mysterious operation.