Extremely intricate (6)
I believe the answer is:
knotty
'extremely intricate' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for knotty that I've seen before include "Tangled - snarled" , "Difficult (like wood hard to chop through?)" , "Complex - hard to solve" , "Gnarled - complicated" , "Tree trunk with hard masses - it's problematic" .)