Difficult adhesive (6)
I believe the answer is:
sticky
I believe this clue is a double definition.
'difficult' is the first definition.
('sticky' can be similar in meaning to 'difficult')
'adhesive' is the second definition.
('sticky' can be similar in meaning to 'adhesive')
(Other definitions for sticky that I've seen before include "Viscous - problematic" , "Warm and humid" , "Adhesive; awkward" , "Glutinous, gooey" , "Twiggy" .)