Unit of stamps (5)
I believe the answer is:
sheet
'unit of stamps' is the definition.
(I've seen this in another clue)
This is the entire clue.
(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]" .)