Design curtains (3)
I believe the answer is:
end
I believe this is a double definition.
'design' is the first definition.
(both can mean a purpose or goal)
'curtains' is the second definition.
(I've seen this in another clue)
(Other definitions for end that I've seen before include "Purpose, objective" , "Objective or conclusion" , "Bring to a close" , "SECOND PART OF 10" , "Finish, close" .)