Thing's purpose (6)
I believe the answer is:
object
I believe this is a double definition.
'thing's' is the first definition.
(I've seen this in another clue)
'purpose' is the second definition.
(I've seen this before)
(Other definitions for object that I've seen before include "Idea" , "Express opposition; goal" , "oppose" , "State opposition" , "Protest; purpose; thing" .)