Diaries intermittently revealing anger (3)
I believe the answer is:
ire
'anger' is the definition.
(I've seen this before)
'diaries intermittently' is the wordplay.
'intermittently' means one should take alternating letters.
The alternate letters of 'diaries' are 'IRE'.
'revealing' is the link.
(Other definitions for ire that I've seen before include "Choler" , "Hot temper" , "Anger, rage" , "'Anger, wrath (3)'" , "Anger, annoyance" .)