Heiress's passion (3)

I believe the answer is:

ire

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'passion' is the definition.
(ire is passionate anger)

'heiress's' is the wordplay.
'IRE' is hidden within the letters.
But, I am unsure how this is indicated.

Can you help me to learn more?

(Other definitions for ire that I've seen before include "Displeasure" , "Choler" , "passionate feeling" , "resentment" , "Fury" .)

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