Misery of a teacher working with horrible head (9)
I believe the answer is:
heartache
'misery' is the definition.
(thesaurus)
'a teacher working with horrible head' is the wordplay.
'working with' is an anagram indicator (working with the letters).
'head' says to take the initial letters.
The initial letter of 'horrible' is 'h'.
'a'+'teacher'='ateacher'
'ateacher' with its letters mixed up with 'h' can make 'HEARTACHE'.
'of' is the link.
(Other definitions for heartache that I've seen before include "Grief" , "it gives rise to anguish" , "Great sadness" , "Emotional anguish" , "Emotional distress" .)