recondite

secret; dead secret, profound secret; arcanum, mystery; latency; sealed book, secrets of the prison house; le desous des cartes., enigma, riddle, puzzle, nut to crack, conundrum, charade, rebus, logogriph; monogram, anagram; Sphinx; crux criticorum., maze, labyrinth, Hyrcynian wood; intricacy, meander., problem (question); paradox (difficulty); unintelligibilty; terra incognita (ignorance).

secret (concealed); involved, [more]; labryrinthian, mazy.