Aim to protest (6)
I believe the answer is:
object
I believe this clue is a double definition.
'aim' is the first definition.
(I know that aim can be written as object)
'protest' is the second definition.
(as in objecting to something)
'to' acts as a link.
(Other definitions for object that I've seen before include "Make protest, disagree" , "Tangible thing" , "Take exception to the thing" , "Voice disapproval; goal" , "Aim or purpose" .)