Fervor (4)
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I believe the answer is:
zeal
'fervor' is the definition.
(I know that zeal is a type of fervor)
This is all the clue.
(Other definitions for zeal that I've seen before include "Fanaticism" , "Zest, ardour" , "Verve" , "Eagerness and devotion" , "(Excessive) fervour" .)