Undefined organisation? (6,7)
I believe the answer is:
united nations
'organisation?' is the definition.
(United Nations is an example)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for united nations that I've seen before include "peace group" , "International peace-keeping organisation" , "body" , "International peace organisation, founded 1945 in San Francisco" , "global organisation" .)