Protest about naughty form of government (9)
I believe the answer is:
democracy
'form of government' is the definition.
(democracy is a kind of form of government)
'protest about naughty' is the wordplay.
'protest' becomes 'demo' (I've seen this before).
'about' becomes 'c' (abbreviation for 'circa'**).
'naughty' becomes 'racy' ('racy' can be a synonym of 'naughty').
'demo'+'c'+'racy'='DEMOCRACY'
(Other definitions for democracy that I've seen before include "The least worst political system?" , "form of government" , "Government of/by/for all the people" , "expression of popular will?" .)