Lumpy, gnarled (6)
I believe the answer is:
knotty
I believe this is a double definition.
'lumpy' is the first definition.
(thesaurus)
'gnarled' is the second definition.
(I know that gnarled can be written as knotty)
(Other definitions for knotty that I've seen before include "Full of tangles; extremely intricate" , "Difficult (point)" , "Very difficult - complex" , "Difficult - having hard lumps (of wood)" , "puzzling" .)