Pain of teachers (4)
I believe the answer is:
ache
'pain' is the definition.
(ache is a kind of pain)
'of teachers' is the wordplay.
'of' says the answer is hidden in the clue.
'ACHE' is hidden in the letters of 'teachers'.
(Other definitions for ache that I've seen before include "Cause pain" , "strong feeling" , "Feel sore" , "Throb - hurt" , "Pine" .)