Strong feeling, occasionally fierce (3)

I believe the answer is:

ire

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

'occasionally fierce' is the wordplay.
'occasionally' indicates alternate letters.
The alternating letters of 'fierce' are 'IRE'.

(Other definitions for ire that I've seen before include "Anger, annoyance" , "Irritation, anger" , "Intense anger" , "passion" , "Anger, rage" .)

I've seen this clue in The Times.

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