What's concealed in parchment is cunning (4)
I believe the answer is:
arch
'cunning' is the definition.
(I've seen this before)
'what's concealed in parchment is' is the wordplay.
'what's concealed in' indicates a hidden word.
'ARCH' is hidden within 'parchment is'.
(Other definitions for arch that I've seen before include "Construction with a keystone" , "Structure with a keystone" , "Affectedly playful like curved structure" , "Chief - part of foot" , "Curved span" .)