Resentment's highest point, reportedly (5)
I believe the answer is:
pique
'resentment's' is the definition.
(thesaurus)
'highest point reportedly' is the wordplay.
'highest point' becomes 'peak' (I've seen this before).
'reportedly' shows a homophone (sound like).
'peak' is a homophone of 'PIQUE'.
(Other definitions for pique that I've seen before include "Ill-feeling; fabric" , "Offence taken" , "Feeling of wounded pride" , "Equip (anag.)" , "Arouse" .)