arcana

Etymology

From Latin arcānus (“hidden, secret”), from arcēre (“to withhold”), arca (“a chest”).

noun

1. Specialized knowledge that is mysterious to the uninitiated.
   Thou deign'st no answer,—or I fain would ask If since thy bright creation, thou hast seen Ought like a Newton, whose admitted eye The arcana of the universe explored Light's subtle ray its mechanism disclosed, The impetuous comet his mysterious lore Unfolded, 1827, Lydia Sigourney, Poems, To the Moon, page 15
   This is not, however, a mere salmagundi of alphabetical arcana. 14 September 2013, Jane Shilling, “The Golden Thread: the Story of Writing, by Ewan Clayton, review [print edition: Illuminating language]”, in The Daily Telegraph (Review), page R29

noun

1. plural of arcanum