Season Six avoids tax, originally set around Luxembourg (4)
I believe the answer is:
Here is my best explanation:
'season' is the definition.
(salting is a kind of seasoning)
'six avoids tax originally set around luxembourg' is the subsidiary indication.
'originally' says to take the initial letters.
'set' indicates anagramming the letters (instruction to set the letters).
'around' indicates putting letters inside.
'luxembourg' becomes 'l' (international vehicle registration code).
The first letters of 'six avoids tax' is 'sat'.
'sat' is an anagram of 'sat'.
'sat' enclosing 'l' is 'salt'.
(Other definitions for salt that I've seen before include "Crystalline substance used to season food", "Mariner; sodium chloride", "Crystalline substance for the table", "Wit; sodium chloride", "Preservative", "A condiment", "White crystalline substance", "Brackish", "Sailor" and "Sea dog".)