Paper that deceives crown? (8)
I believe the answer is:
foolscap
'paper' is the definition.
(foolscap is a kind of paper)
'deceives crown?' is the wordplay.
'deceives' becomes 'fools' (fooling is a kind of deceiving).
'crown?' becomes 'cap' ('cap' can be a synonym of 'crown').
'fools'+'cap'='FOOLSCAP'
'that' acts as a link.
(Other definitions for foolscap that I've seen before include "something near A4" , "Paper or book size (from its watermark)" , "type of paper" , "One would not be wise to put this on" , "sheet" .)