Leave behind urn? (6)
I believe the answer is:
outrun
'leave behind' is the definition.
(thesaurus)
I cannot understand how the remainder of the clue works.
(Other definitions for outrun that I've seen before include "Go faster than, on the gallop" , "Go faster than as in foot race" , "Be too fast for on foot" , "Overtake, escape" , "Lose" .)