arcane

The word 'arcane' entered English in the 16th century from the Latin adjective 'arcanus', meaning 'secret, hidden, private'. This Latin term is derived from 'arca', meaning 'chest, box', which is the source of the English word 'ark'. The semantic logic is clear: just as valuables are concealed within a chest, arcane knowledge is hidden from general view. The Latin 'arca' itself is traced back to the Proto-Indo-European root h₂erk-, meaning 'to hold, contain, guard', linking the concept of secrecy to that of protection and enclosure.

The word is a simplex loanword from Latin. It cannot be meaningfully segmented into smaller, independent morphemes using its modern English spelling.