Pole identifies Welsh runner (9)
I believe the answer is:
flagstaff
'pole' is the definition.
(thesaurus)
'identifies welsh runner' is the wordplay.
'identifies' becomes 'flags'.
'welsh runner' becomes 'taff' (Welsh river, so something that 'runs').
'flags'+'taff'='FLAGSTAFF'
(Other definitions for flagstaff that I've seen before include "somewhere in Arizona" , "place in Arizona" , "Arizona city" , "Ceremonial pole" , "supporter of Jack?)" .)