Choose examination of voters (9)
I believe the answer is:
electoral
'of voters' is the definition.
(I've seen this before)
'choose examination' is the wordplay.
'choose' becomes 'elect' (electing is a kind of choosing).
'examination' becomes 'oral' (oral is a kind of examination).
'elect'+'oral'='ELECTORAL'
(Other definitions for electoral that I've seen before include "Regarding choices" , "type of roll" , "on the voting register" , "Like sort of college" , "of constituents" .)