Archdeacon always in disguise (6)
I believe the answer is:
veneer
'disguise' is the definition.
(I've seen this before)
'archdeacon always' is the wordplay.
'archdeacon' becomes 'ven'.
'always' becomes 'eer' (poetic way of saying ever).
'ven'+'eer'='VENEER'
'in' acts as a link.
(Other definitions for veneer that I've seen before include "Thin wooden surface" , "Outward respectability" , "A surface coating or skin" , "Superficial veneer" , "Finish" .)