Swiss city on the Rhine (5)
(Other definitions for basle that I've seen before include "Swiss city and canton" , "Canton of NW Switzerland" , "Swiss city for sable?" , "Canton of N W Switzerland" , "European city" .)
'swiss city on the rhine' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for basel that I've seen before include "In European city" , "Swiss city" , "City of Switzerland" .)