New to being employed by the UN (6)
I believe the answer is:
unused
'new to' is the definition.
(thesaurus)
'employed by the un' is the wordplay.
'employed' becomes 'used' ('use' can be a synonym of 'employ').
'by' says to put letters next to each other.
'used' put after 'un' is 'UNUSED'.
'being' is the link.
(Other definitions for unused that I've seen before include "Pristine" , "Surplus" , "Not accustomed to" , "Left over" , "hadn't been exploited" .)