Heiress’s passion (3)

I believe the answer is:

ire

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'passion' is the definition.
(I've seen this before)

'heiress's' is the wordplay.
'IRE' is hidden in amongst the letters.
However, 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 "Displeasure" , "Choler" , "passionate feeling" , "resentment" , "Fury" .)

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