A French right to be wrong (6)
I believe the answer is:
untrue
'be wrong' is the definition.
('untrue' can be a synonym of 'wrong')
'a french right' is the wordplay.
'a french' becomes 'un' ('a' in French).
'right' becomes 'true' ('true' is associated in meaning with 'right'**).
'un'+'true'='UNTRUE'
'to' is the link.
(Other definitions for untrue that I've seen before include "Not factual or honest" , "Not level" , "apocryphal" , "Not loyal" , "Not in accordance with fact" .)