Unit of stamps (5)
I believe the answer is:
sheet
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">unit of stamps</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 sheet that I've seen before include "Piece of paper or bedding" , "Piece of paper or bedlinen" , "Whence to sing hymns?" , "leaf" , "* [MATERIAL]" .)