making great mental demands; hard to comprehend or solve or believe
"a baffling problem"
"I faced the knotty problem of what to have for breakfast"
"a problematic situation at home"
highly complex or intricate and occasionally devious
"the Byzantine tax structure"
"Byzantine methods for holding on to his chairmanship"
"convoluted legal language"
"convoluted reasoning"
"the plot was too involved"
"a knotty problem"
"got his way by labyrinthine maneuvering"
"Oh, what a tangled web we weave"
"tortuous legal procedures"
"tortuous negotiations lasting for months"
Full of knots.