Reason news boss is finished (5)
I believe the answer is:
ended
'is finished' is the definition.
(similar in meaning)
'reason news boss' is the wordplay.
'reason' becomes 'end' (I've seen this in other clues).
'news boss' becomes 'ed' (short for editor).
'end'+'ed'='ENDED'
(Other definitions for ended that I've seen before include "Brought to a close" , "Finished, terminated" , "Broke off; finished" , "'Our revels now are . . . . .' (The Tempest)" , "Stopped" .)