Difficult experimentation (7)
I believe the answer is:
testing
I believe this is a double definition.
'difficult' is the first definition.
(I've seen this before)
'experimentation' is the second definition.
(I know that testing is a type of experimentation)
(Other definitions for testing that I've seen before include "of a difficult nature" , "stressful" , "tiresome" , "Examining" , "Trying out" .)