Reveal United Nations disguise (7)
I believe the answer is:
uncover
'reveal' is the definition.
(synonyms)
'united nations disguise' is the wordplay.
'united nations' becomes 'UN' (synonyms).
'disguise' becomes 'cover' (I've seen this in another clue).
'un'+'cover'='UNCOVER'
(Other definitions for uncover that I've seen before include "bare" , "Strip off" , "Expose, unveil" , "make a revelation" , "Expose, reveal" .)