Quantity of paper (4)
'quantity of paper' is the definition.
(a ream is a large amount of paper)
This is the entire clue.
(Other definitions for ream that I've seen before include "480 sheets of paper" , "Widen (hole) with borer; twenty quires" , "516 sheets of paper" , "Many sheets - enlarge hole" , "Make hole larger - lot of paper" .)
'quantity of paper' is the definition.
(unit for a large amount of paper)
This is all the clue.
(Other definitions for quire that I've seen before include "Quantity of paper" , "Twentieth part of a ream" , "One-twentieth of a ream" , "A number of paper sheets" , "Measure of writing paper" .)