Don't agree to a thing! (6)
I believe the answer is:
object
I believe this clue is a double definition.
'don't agree' is the first definition.
(I've seen this before)
'a thing' is the second definition.
(I know that object is a type of Thing)
'to' acts as a link.
(Other definitions for object that I've seen before include "Express dislike - article" , "Thing; complain" , "Express dissent, protest" , "deplorable spectacle" , "end" .)