Paper purchase (4)
I believe the answer is:
ream
'paper purchase' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for ream that I've seen before include "Widen (hole) with borer; twenty quires" , "Make hole larger - lot of paper" , "Widen out (bore)" , "Twenty quires of paper" , "500 sheets, perhaps" .)