Relax after a French victory over Germany (6)
I believe the answer is:
unwind
'relax' is the definition.
('unwind' can be a synonym of 'relax')
'a french victory over germany' is the wordplay.
'a french' becomes 'un' ('a' in French).
'victory' becomes 'win' (I've seen this before).
'over' means one lot of letters go next to another.
'germany' becomes 'd' (international vehicle registration code).
'un'+'win'+'d'='UNWIND'
'after' is the link.
(Other definitions for unwind that I've seen before include "Straighten out like snake" , "Relax like spring?" .)