complexity (n.)

• abstruseness
• arduousness
• burdensomeness
• complication
• convolution
• crabbedness
• deepness
• difficultness
• difficulty
• esoterica
• hairiness
• hardness
• inscrutability
• intricacy
• involvement
• knottiness
• laboriousness
• onerousness
• oppressiveness
• profoundness
• profundity
• reconditeness
• rigor
• rigorousness
• ruggedness
• strenuousness
• toilsomeness
• toughness
• troublesomeness