Smart Conservative overcoming Left always (6)
I believe the answer is:
clever
'smart' is the definition.
(similar in meaning)
'conservative overcoming left always' is the wordplay.
'conservative' becomes 'C' (UK political abbreviation).
'overcoming' is a charade indicator (letters next to each other) (some letters are written over others).
'left' becomes 'l' (common abbreviation).
'always' becomes 'ever' (synonyms).
'c'+'l'+'ever'='CLEVER'
(Other definitions for clever that I've seen before include "Sharp-witted, intelligent" , "Smart, adroit" , "Mentally quick and resourceful" , "Gifted" , "Highly intelligent" .)