Terminated some of proven dedication (5)
I believe the answer is:
ended
'terminated' is the definition.
('end' can be a synonym of 'terminate')
'some of proven dedication' is the wordplay.
'some of' indicates a hidden word.
'ENDED' is hidden in the letters of 'proven dedication'.
(Other definitions for ended that I've seen before include "Finished, terminated" , "Stopped" , "Ceased" , "died" , "wound up" .)