Block of paper (3)
I believe the answer is:
pad
'block of paper' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for pad that I've seen before include "protection for member" , "Guard against impact" , "Footprint - home of one's own (slang)" , "Fill with extra material in order to lengthen" , "Floating leaf of a lily" .)