Difficult, tiresome (6)
I believe the answer is:
trying
This clue is a double definition.
'difficult' is the first definition.
(similar in meaning)
'tiresome' is the second definition.
(trying can mean annoying or tiresome)
(Other definitions for trying that I've seen before include "Aggravating" , "Upsetting" , "Stressful" , "irksome" , "Taxing" .)