As slang, it's finished (5)
I believe the answer is:
kaput
'it's finished' is the definition.
(synonyms)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for kaput that I've seen before include "Broken down irretrievably" , "Ruined (slang)" , "Broken, done for" , "Permanently broken" , "Broken or finished - in Germany" .)