Relaxes German and secures victory - success at last (7)
I believe the answer is:
unwinds
'relaxes' is the definition.
('unwind' can be a synonym of 'relax')
'german and secures victory success at last' is the wordplay.
'german and' becomes 'und' ('and' in German).
'secures' indicates putting letters inside.
'victory' becomes 'win' (I've seen this before).
'at last' indicates one should take the final letters.
The final letter of 'success' is 's'.
'und' placed around 'win' is 'unwind'.
'unwind'+'s'='UNWINDS'
(Other definitions for unwinds that I've seen before include "Rests and becomes less tense" , "Becomes less tense and relaxes" , "Relaxes; pays out (thread)" .)