Disagreement with a New York jeweller (7)
I believe the answer is:
tiffany
'jeweller' is the definition.
(Tiffany and Co. is an American jewelry company)
'disagreement with a new york' is the wordplay.
'disagreement' becomes 'tiff' (tiff is a kind of disagreement).
'with' means one lot of letters go next to another.
'new york' becomes 'ny'.
'tiff'+'a'+'ny'='TIFFANY'
(Other definitions for tiffany that I've seen before include "like a sort of glass" , "US glass designer" , "Girl's name - New York jeweller" , "fine fabric" , "Transparent" .)