Groan joining Tory leader's vision (5)
I believe the answer is:
sight
'vision' is the definition.
('sight' can be a synonym of 'vision')
'groan joining tory leader's' is the wordplay.
'groan' becomes 'sigh' (I've seen this before).
'joining' is a charade indicator (letters next to each other).
'tory leader' becomes 't' (I've seen this in other clues).
'sigh'+'t'='SIGHT'
(Other definitions for sight that I've seen before include "A great many" , "good deal" , "Looking" , "Notice" , "View" .)