Opinions still extremely tedious (8)
I believe the answer is:
thoughts
'opinions' is the definition.
('thought' can be a synonym of 'opinion')
'still extremely tedious' is the wordplay.
'still' becomes 'though'.
'extremely' means to remove the middle letters (only the extremes of the word are used).
'tedious' with its middle taken out is 'ts'.
'though'+'ts'='THOUGHTS'
(Other definitions for thoughts that I've seen before include "Cogitations" , "Ideas and opinions (8)" , "Notions" , "Ideas, reflections" , "They are in my mind" .)