Heiress's passion (3)

I believe the answer is:

ire

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

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

'heiress's' is the wordplay.
'IRE' is hidden in amongst the letters.
But, I am unsure how the hidden word 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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