Paper tray unit (5)
I believe the answer is:
sheet
'paper tray unit' 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 "One of pair tucked in" , "Sail-rope on the bed?" , "Page of postage stamps" , "Piece of paper; nautical rope" , "Bedcover" .)