Hair treatment provided by barber in Seville (5)
I believe the answer is:
rinse
'hair treatment' is the definition.
(I've seen this in another clue)
'provided by barber in seville' is the wordplay.
'provided by' indicates a hidden word (the answer is provided within the clue).
'RINSE' can be found hidden inside 'barber in seville'.
(Other definitions for rinse that I've seen before include "Flush" , "blue one on top?" , "Remove soap with clean water" , "Mouth cleansing solution" , "Wash - siren (anag)" .)