Fireman internalises wrath (3)

I believe the answer is:

ire

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'wrath' is the definition.
(both can mean anger)

'fireman internalises' is the wordplay.
'IRE' is hidden within the letters.
But, I'm not sure how this is indicated.

Can you help me to learn more?

(Other definitions for ire that I've seen before include "passionate feeling" , "Outrage" , "Paddy" , "resentment" , "Losing head" .)

I've seen this clue in The Mirror.

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