Beverage server (3)
I believe the answer is:
'beverage server' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for urn that I've seen before include "Tall vase with stem" , "Vase; tea vessel" , "Vessel for tea or ashes" , "A vase, as for holding human ashes" , "Run to get large jar" .)