Anger in answering back (3)
I believe the answer is:
ire
'anger' is the definition.
(ire is intense rage)
'in answering back' is the wordplay.
'in' says the answer is hidden in the clue.
'back' says the letters should be written in reverse.
'eri' can be found hidden inside 'answering'.
'eri' back-to-front is 'IRE'.
(Other definitions for ire that I've seen before include "Intense anger" , "Strong emotion" , "Anger, rage" , "Outrage" , "Hot temper" .)