Swiss canton (6)
'swiss canton' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for lucerne that I've seen before include "Swiss city/lake" , "Alfalfa - Swiss lake and resort" , "Clover-like plant used for fodder" , "edible plant" , "Fodder crop - lake" .)
(Other definitions for zurich that I've seen before include "Swiss financial centre" , "Swiss financial capital" , "See 8" , "Swiss banking centre" , "Swiss city noted for gnomes" .)