Stopped sad EEC regenerating (6)
I believe the answer is:
ceased
'stopped' is the definition.
('cease' can be a synonym of 'stop')
'sad eec regenerating' is the wordplay.
'regenerating' indicates an anagram.
'sad'+'eec'='sadeec'
'sadeec' with letters rearranged gives 'CEASED'.
(Other definitions for ceased that I've seen before include "Stopped, quitted" , "Finished" , "Came to a close" , "Stopped, ended" , "Stopped or discontinued" .)