Obscure papers concealed by ambassador (4)
I believe the answer is:
hide
'obscure' is the definition.
('hide' can be a synonym of 'obscure')
'papers concealed by ambassador' is the wordplay.
'papers' becomes 'id' (identification papers).
'concealed by' is an insertion indicator.
'ambassador' becomes 'he' (His or Her Excellency).
'id' inserted inside 'he' is 'HIDE'.
(Other definitions for hide that I've seen before include "Flog" , "Mammal's tough skin" , "Animal's tough skin" , "go to ground" , "harbour" .)