knotty
[adjective]
Synonyms: complex, Byzantine, complicated, daedal, elaborate, gordian, intricate, involved, labyrinthine, sophisticated, hard, difficult, effortful, formidable, rough, rugged, sticky, terrible, tough, uphill

[TahlilGaran] English Synonym Dictionary ▲

knot‧ty /ˈnɒti $ ˈnɑːti/ adjective

1. difficult to solve:
a knotty problem

2. knotty wood contains a lot of hard round places where branches once joined the tree

[TahlilGaran] Dictionary of Contemporary English ▲