Passion occasionally ardent in pretty pass (7)

I believe the answer is:

madness

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'passion' is the definition.
(thesaurus)

'occasionally ardent in pretty pass' is the wordplay.
'occasionally' means one should take alternating letters (letters taken at regular intervals or occasions).
'in' indicates putting letters inside.
'pretty pass' becomes 'mess' (I can't explain this - if you can you should believe this answer much more).
The alternate letters of 'ardent' are 'adn'.
'adn' placed within 'mess' is 'MADNESS'.

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(Other definitions for madness that I've seen before include "Lunacy - ska/pop band" , "Irrationality" , "Dementia" , "Utter foolishness" , "hysteria?" .)

I've seen this clue in The Telegraph.

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