Used to describe something known or understood by only a few.
El significado del arcano se ha perdido a lo largo de los siglos, dejando muchas preguntas sin respuesta.
The meaning of the arcane has been lost over the centuries, leaving many questions unanswered.
Los secretos del antiguo libro eran tan arcanos que pocos podían comprenderlos.
The secrets of the ancient book were so arcane that few could understand them.