Paper size (4)
'paper size' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for foolscap that I've seen before include "Cop's foal (anag)" , "sheet" , "type of paper" , "something near A4" , "Paper or book size (from its watermark)" .)
'paper size' is the definition.
(I've seen this in another clue)
This is the entire clue.