Season Six avoids tax, originally set around Luxembourg (4)
I believe the answer is:
salt
'season' is the definition.
(salting is a kind of seasoning)
'set around luxembourg' is the wordplay.
'set' becomes 'sat' (I am not sure about this - if you are sure you should believe this answer much more).
'around' is an insertion indicator.
'luxembourg' becomes 'l' (international vehicle registration code).
'sat' enclosing 'l' is 'SALT'.
'six avoids tax originally' is the link.
This may not be right. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for salt that I've seen before include "White crystalline substance" , "Pile up" , "dry wit" , "Wit; sodium chloride" , "Crystalline substance used to season food" .)