Ending unfortunately so cruel (7)
I believe the answer is:
closure
'ending' is the definition.
(closure is a kind of ending)
'unfortunately so cruel' is the wordplay.
'unfortunately' indicates an anagram.
'so'+'cruel'='socruel'
'socruel' is an anagram of 'CLOSURE'.
(Other definitions for closure that I've seen before include "Settlement giving psychological satisfaction" , "Feeling of emotional resolution" , "End; fastening" , "end of debate" , "Lose cur (anag.)" .)