Synonyms and related words :
abstruseness, arduousness, bothersomeness, burdensomeness, complexity, complexness, complication, convolution, crabbedness, crampedness, deepness, difficultness, difficulty, entanglement, esoterica, hairiness, hardness, intricateness, involution, involvement, knottiness, laboriousness, onerousness, oppressiveness, perplexity, profoundness, profundity, ramification, reconditeness, rigor, rigorousness, ruggedness, strenuousness, subtlety, tanglement, technicality, toilsomeness, toughness, troublesomeness