Finished making true advance (8)
I believe the answer is:
overture
'advance' is the definition.
('overture' can be a synonym of 'advance')
'finished making true' is the wordplay.
'finished' becomes 'over' ('over' can be similar in meaning to 'finished').
'making' indicates anagramming the letters.
'true' anagrammed gives 'ture'.
'over'+'ture'='OVERTURE'
(Other definitions for overture that I've seen before include "10 {COMPOSITION]" , "eg 'The Hebrides'" , "musical composition" , "Approach - musical introduction" , "Introductory music" .)