Smart bar to east of Croatia's capital (6)
I believe the answer is:
clever
'smart' is the definition.
(similar in meaning)
'bar to east of croatia's capital' is the wordplay.
'bar' becomes 'lever' (lever is a kind of bar).
'to east of' says to put letters next to each other (some letters go to the right of others).
'capital' says to take the initial letters.
The first letter of 'croatia' is 'c'.
'lever' after 'c' is 'CLEVER'.
(Other definitions for clever that I've seen before include "Knowledgeable" , "Smart or shrewd" , "Quick, skilful" , "brilliant" , "Quick at learning, bright" .)