Problematic (6)
'problematic' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for thorny that I've seen before include "Problematic; spiny" , "Difficult; prickly" , "Bristling with perplexities" , "Covered in spikes" , "Trying" .)
(Other definitions for tricky that I've seen before include "Complicated" , "Thorny" , "Crafty, foxy, slippery" , "Crafty or difficult" , "Awkwardly difficult" .)