Protest against something (6)
I believe the answer is:
object
This clue is a double definition.
'protest against' is the first definition.
(thesaurus)
'something' is the second definition.
(thesaurus)
(Other definitions for object that I've seen before include "Express dislike - article" , "Thing; demur" , "Express dissent, protest" , "design?" , "Protest, disapprove" .)