Difficult, intricate (6)
I believe the answer is:
knotty
I believe this clue is a double definition.
'difficult' is the first definition.
(similar in meaning)
'intricate' is the second definition.
(synonyms)
(Other definitions for knotty that I've seen before include "Gnarled - complicated" , "Pinewood can be" , "Difficult (like wood hard to chop through?)" , "Difficult (point)" , "Describing a difficult problem" .)