Peacekeeping body has right to vessel (3)
I believe the answer is:
urn
'to vessel' is the definition.
(urn is a type of container)
'peacekeeping body has right' is the wordplay.
'peacekeeping body' becomes 'un' (I can't justify this - if you can you should believe this answer much more).
'has' indicates putting letters inside.
'right' becomes 'r' (common abbreviation).
'un' going around 'r' is 'URN'.
Can you help me to learn more?
(Other definitions for urn that I've seen before include "Vase with handles" , "Ashes trophy" , "Large vase for holding ashes of dead person" , "Container for tea or ashes" , "Without cost; last word of Tempest" .)