Time to treat mentor's anguish (7)
I believe the answer is:
torment
'anguish' is the definition.
(tormenting is a kind of anguishing)
'time to treat mentor's' is the wordplay.
'time' becomes 't'.
'to treat' indicates anagramming the letters.
'mentor' with letters rearranged gives 'orment'.
't'+'orment'='TORMENT'
(Other definitions for torment that I've seen before include "Extreme mental or physical distress" , "Severe physical or mental suffering" , "Tease unkindly" , "Inflict pain on - pester" , "Pester or tease unmercifully" .)