What is another word for "ignorance"?

Roget's Thesaurus (1911) lists these synonyms for "ignorance": anagram, arcanum, book, charade, concealed, confidential, conundrum, crack, crux, dead, difficulty, enigma, house, incognita, intricacy, involved, labyrinth, labyrinthian, labyrinthine, latency, logogriph, maze, mazy, meander, monogram, mystery, nut, paradox, prison, problem, profound, puzzle, question, rebus, riddle, secret, terra, the, top, wood.