He heartens Hiram (3)

I believe the answer is:

ira

I'm a little stuck... Click here to teach me more about this clue!

'he' is the definition.

'heartens hiram' is the wordplay.
'IRA' is hidden within the letters.
But, I am not sure how this is indicated.

Can you help me to learn more?

(Other definitions for ira that I've seen before include "Illegal organisation, in short" , "George 13 down's brother" , "Militant Irish nationalist organisation" , "Militant republicans" , "Gershwin, say" .)

I've seen this clue in the Evening Standard.

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