Synonyms and related words :
abstruseness, arcanum, cabala, classified information, complexity, complication, confidence, confidential communication, crabbedness, crampedness, deepness, difficulty, enigma, guarded secret, hardness, hermetics, intricacy, knottiness, mystery, mystery of mysteries, personal matter, private matter, privileged communication, privity, profound secret, profoundness, profundity, reconditeness, restricted information, sealed book, secret, the occult