Argue about borders for another import tax (6)
I believe the answer is:
tariff
'import tax' is the definition.
(thesaurus)
'argue about borders for another' is the wordplay.
'argue' becomes 'tiff' (tiff can mean to argue).
'about' means one lot of letters goes inside another.
'borders for' says to hollow out the word (remove centre letters) (only the letters at the borders of the word).
'another' with its middle taken out is 'ar'.
'tiff' placed around 'ar' is 'TARIFF'.
(Other definitions for tariff that I've seen before include "Import duty, tax" , "List of duties on imports or exports" , "Rate" , "Import/export tax" , "Table of (hotel) charges" .)