First person regarding anger (3)
I believe the answer is:
ire
'anger' is the definition.
(ire is intense rage)
'first person regarding' is the wordplay.
'first person' becomes 'i' (first-person pronoun).
'regarding' becomes 're' (re can mean regarding, concerning).
'i'+'re'='IRE'
(Other definitions for ire that I've seen before include "Losing head" , "resentment" , "Fury" , "Strong feeling" , "Hot temper" .)