One about to reveal anger (3)
I believe the answer is:
ire
'anger' is the definition.
(ire is intense rage)
'one about' is the wordplay.
'one' becomes 'i' (Roman numeral).
'about' becomes 're' ('re' means regarding or about).
'i'+'re'='IRE'
'to reveal' acts as a link.
(Other definitions for ire that I've seen before include "Hot temper" , "Irritation, anger" , "Fury" , "passion" , "exasperation" .)