Smart Conservative at bar (6)
I believe the answer is:
clever
'smart' is the definition.
(similar in meaning)
'conservative at bar' is the wordplay.
'conservative' becomes 'C' (UK political abbreviation).
'at' means one lot of letters go next to another.
'bar' becomes 'lever' (lever is a kind of bar).
'c'+'lever'='CLEVER'
(Other definitions for clever that I've seen before include "Bright; smart" , "Smar and canny" , "& 18 Down Smart Alec" , "expert" , "Bright, quick-witted, intelligent" .)