Greens almost get behind Conservative group (7)
I believe the answer is:
cabbage
'greens' is the definition.
(thesaurus)
'almost get behind conservative group' is the wordplay.
'almost' means to remove the last letter (almost the whole word is kept).
'behind' is a charade indicator (letters next to each other).
'conservative' becomes 'C' (UK political abbreviation).
'group' becomes 'abba' (pop group).
'get' with its final letter taken off is 'ge'.
'c'+'abba'='cabba'
'ge' put after 'cabba' is 'CABBAGE'.
(Other definitions for cabbage that I've seen before include "Kind of 13" , "Main ingredient of sauerkraut" , "Vegetable with dense head of leaves" , "Veg" , "Beg a cab for the strange vegetable" .)