Unhappy mix, resulting in case of discord (11)
I believe the answer is:
disgruntled
'unhappy' is the definition.
(thesaurus)
'mix resulting in case of discord' is the wordplay.
'mix' indicates an anagram.
'in' means one lot of letters goes inside another.
'case of' says to hollow out the word (remove centre letters) (outsides of).
'discord' with its centre removed is 'dd'.
'resulting' anagrammed gives 'isgruntle'.
'isgruntle' inserted into 'dd' is 'DISGRUNTLED'.
(Other definitions for disgruntled that I've seen before include "Cheesed off" , "Grumpy" , "Angry or dissatisfied" , "Sulking" , "Sulky" .)