Politician says piece (9)
I believe the answer is:
statesman
'politician' is the definition.
(statesman is a kind of politician)
'says piece' is the wordplay.
'says' becomes 'states' ('state' can be a synonym of 'say').
'piece' becomes 'man' ('man' can be a synonym of 'piece'**).
'states'+'man'='STATESMAN'
(Other definitions for statesman that I've seen before include "Experienced politician" , "Respected politician" , "Leading politician" , "Government minister" , "Distinguished politician" .)