Venerable Australian state capital (7)
I believe the answer is:
augusta
'state capital' is the definition.
(state capital of Maine)
'venerable australian' is the wordplay.
'venerable' becomes 'august' (synonyms).
'australian' becomes 'A' (common abbreviation).
'august'+'a'='AUGUSTA'
(Other definitions for augusta that I've seen before include "22 [MAINE] 's capital" , "US state capital - girl's name" , "American city" , "Female name; capital of state of Maine" , "Place in Georgia" .)