Speaking in public once before a politician (7)
I believe the answer is:
oratory
'speaking in public' is the definition.
(oratory means public speaking)
'once before a politician' is the wordplay.
'once before' becomes 'or' (I've seen this in other clues).
'politician' becomes 'tory' (term for a Conservative Party politician).
'or'+'a'+'tory'='ORATORY'
(Other definitions for oratory that I've seen before include "Rhetorical language" , "Cicero's art" , "Small chapel for private worship" , "Art of public speaking or small chapel" , "Rhetoric - place of prayer" .)