Cancel an international body function (4)
I believe the answer is:
undo
'cancel' is the definition.
(I've seen this before)
'an international body function' is the wordplay.
'an international body' becomes 'UN' (short for United Nations).
'function' becomes 'do' (I've seen this in other clues).
'un'+'do'='UNDO'
(Other definitions for undo that I've seen before include "Ruin prospects of; cancel" , "Open or unfasten" , "Disentangle" , "Release fastening" , "Loosen or reverse" .)