Amount of paper (4)
I believe the answer is:
ream
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">amount of paper</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for ream that I've seen before include "Widen (hole); quantity of paper" , "Five hundred sheets of paper" , "Quantity of paper, about 500 sheets" , "Lots of paper" , "480 sheets of paper" .)